After 3 years investment of 1200 compounded annually and an interest rate R will yield an amount of 1200 (1+R)Q
write this polynomial in standard form
a(r) = 1200 (1+r)^3
Now just expand the binomial power.
a(r) = 1200(r^3 + 3r^2 + 3r + 1)
and multiply through by 1200