Answer: 64%

From the integrated rate law for a first order reaction, $ [A] = [A]_0\; e^{-kt}$.

The fraction remaining is the concentration divided by the initial concentration $ = \large\frac{[A]}{[A_0]}$$ = e^{2.95 \times 10^{-3} s^{-1} \times 150\; s}$$ = 0.642$ or $64\%$