How to find increasing and decreasing intervals of a function with fraction?

F(x)=x/2-2 and g(x)=2x^2+x-3 find (f+g)(x)

Barbara deposited $300 in the bank. if the bank pays her simple interest at the rate of 4 percent per year, how much money will she have in her account at the end of 9 months?

X+ y = 5 ; x - y =3 solve using linear combination