$2-20$ A building uses electricity for air conditioning in summer months $($June$,$ July, August,

September$)$ and natural gas for space heating in winter months $($October$,$ November, December,

January, February, March, April$).$ Electricity is also used for lighting and running various appliances

throughout the year, while natural gas is also used for water heating throughout the year. Examine the

electricity and natural gas bills on a monthly basis given below.

$($a$)$ Electricity consumption decreases in spring months $($March$,$ April, May$)$ compared to cold

winter months. Why? Explain.

$($b$)$ Estimate the amount and cost of electricity used for air conditioning in summer.

$($c$)$ Estimate the amount and cost of natural gas used for space heating in summer.

$($d$)$ Estimate the amount and cost of natural gas used for water heating.

$($e$)$ Determine the average unit cost of electricity and natural gas. Please give correct answer