In how many years will money quadruple at 8% compounded quarterly?

4x = x (1+.02)^t           x can be any amount, so we'll leave it out.   I per period = 8/4 = .02% per quarter

      How many quarters? (t)

4 = (1.02)^t

log4/log1.02  = t  = 70   QUARTERS = 17.5 years