Clint invested $6000 in a savings account for 12.5 years. at the end of 12.5 years, his savings account had $8250 in it. if $6000 represents p, the principal amount, which percent represents the annual simple interest rate (r) that clint earned after the 12.5 year (t) period?

The balance B at the end of time t is given by
  B = P +Prt
  8250 = 6000 +6000*r*12.5 . . . . substitute the given information
  2250 = 6000*r*12.5 . . . . . . . . . . .subtract 6000
  2250/(6000*12.5) = r . . . . . . . . . .divide by the coefficient of r
  r = .03 = 3%

Clint earned 3% annual simple interest on his savings.