The time required by a mechanic to repair a machine has an exponential distribution with a mean

Question:

The time required by a mechanic to repair a machine has an exponential with a mean of 4 hours. However, a special tool would reduce this mean to 2 hours. If the mechanic repairs a machine in less than 2 hours, he is paid $100; otherwise, he is paid $80. Determine the mechanic’s expected increase in pay per machine repaired if he uses the special tool.
Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...