PLEASE HELP! HURRY!

When we say that an experiment is controlled, we mean that __.

A.) the outcome is certain
B.) the theory has already been supported
C.) there is only one theory being tested by the experiment
D.) there is only one difference between experimental groups

9.9 years

a = p(1 + rt) . . account balance after time t at rate r starting with principal p

3000 = 2500(1 + 0.0202t) . . filling in the given numbers

1.2 = 1 + 0.0202t . . divide by 2500

0.2 = 0.0202t . . . subtract 1

0.2/0.0202 = t ≈ 9.901

it will take about 9.9 years for the account balance to reach $3000.