How do I solve this pls help khan academy is no smart

What is the inverse of the function f(x)=4x+8

1. what is the measure of ∠abc? what is the measure of ∠abd?

The average number of vehicles waiting in line to enter a parking lot can be modeled by the function f left parenthesis x right x squared over 2 left parenthesis 1 minus x right parenthesis endfraction , where x is a number between 0 and 1 known as the traffic intensity. find the rate of change of the number of vehicles waiting with respect to the traffic intensity for the intensities (a) xequals0.3 and (b) xequals0.6.