Let us just follow what you were saying.

in 1990, t = 0, A(0) = 100

in 2002, t = 12, A(12) = 133

And 133 is 33% higher than 100, so in 2002, costs were 33% higher than in 1990.

In what year would the costs be 25% higher than in 1990?

25% higher than 100 = 125, so,

125 = 100e^(0.024t)

e^(0.024t) = 125/100

e^(0.024t) = 1.25

Take ln of both sides,

(0.024t)*ln(e) = ln(1.25)

t = [ln(1.25)]/(0.024) = 9.29765, or say, 9 years.

Therefore, in 1999, the costs are 25% higher than in 1990. ----answer.