Rewrite equation to solve for t:

I=1.5-1.5(10^(-0.03t))

Assuming the left side = 1

-.5 = -1.5(10^(-.03t)
1/3 = 10^(-.03t)
log both sides
log (1/3) = -.03t log 10
-.03t = log1 - log3
t = -log3 /-.03
= ....