I need help with math, cardinal number

Solve for x, y, and z. show all steps.

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)

Players on the school soccer team are selling candles to raise money for an upcoming trip. each player has 24 candles to sell. if a player sells 4 candles a profit of$30 is made. if he sells 12 candles a profit of $70 is made. determine an equation to model his situation?