21-Describe one example of how engineers can reduce the problem of solid waste that is affecting every country around the world.

22-Drinking water can be obtained via (a) bottled spring water or (b) a sink-mounted reverse osmosis device. Briefly discuss two negative aspects of each, from a sustainability point of view.

23-Explain how using less electrical energy in an industrial process is a step toward sustainable engineering.

24-

Some national (e.g., IEEE) standards become international standards. Give one example, citing the original standard and its international counterpart.

25-Name a specific safety standard and explain how it improves safety in Engineering.

26-Some international (e.g., ISO) standards become national standards. Give one example, citing the original standard and its national counterpart.

27-

A and B are negotiating a contract according to which A will develop a system for B. Initially, A says, "I can build the system you described for 500 USD". B says, "You can start the work if you can make it for 300 USD".

A does not respond verbally but goes ahead and does the job. (a) What should B pay once the system is delivered, and (b) why?

28-

A and B signed a contract according to which A will develop a system for B. The contract states the details of the system to be developed, the acceptance criteria, and the delivery schedule. It does, however, not state the amount to be paid by B. (a) Is the contract valid or not, and (b) why?

29-

Consider the following costs associated with all work packages (WP A and WP B) of a project:

WP	Labor hours Type 1	Labor hours Type 2	Labor hours Type 3	Material	Equipment	Subcontracts	Other
A	30	30	10	$500	$100	$8000	$300
B	5	20	60	$200	$1,000	$2000	$400

The rate of labour hours Type 1 is $15.

The rate of labour hours Type 2 is $25.

The rate of labour hours Type 3 is $35.

Calculate the total combined cost of the project showing a breakdown of your calculations.

30-

Consider the project of procuring and installing a grid-tied photovoltaic solar system for a house. The system comprises the following:

• Solar panels for a total capacity of 10kWp
• A 5kVA inverter
• A 10kWh lithium-ion battery
• All accessories for rooftop installation

research to estimate the cost of this project including:

• Procurement
• Installation
• Testing
• Handover

Show the total cost of the system plus a detailed breakdown. Cite your sources such as websites and quotations to support your estimates.