PLS HELP QUICK! 3 x seven tenths

ten twenty ones
twenty four tenths
twenty one thirtieths
twenty one tenths

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

Factor the polynomial by its greatest common monomial factor.

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.