How do you write an expression for Z cubed?

Kathy spent 5/8 of her money on books and another 1/6 of her money on stationeries.what fraction of kathy’s money was left?

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

Richard save $32 in march he saved $48 in april and $38 in may then richard spent $113 on a keyboard how much money does richard have left