Answer
See below.
Work Step by Step
We know that $0.5x=xe^{k\cdot63}\\0.5=e^{63k}\\63k=\ln0.5\\k=\frac{\ln0.5}{63}$
Thus $75=200e^{\frac{\ln0.5}{63}\cdot t}\\0.375=e^{\frac{\ln0.5}{63}\cdot t}\\\frac{\ln{0.5}}{63}t=\ln{0.375}\\t=\frac{\ln{0.375}}{\frac{\ln{0.5}}{63}}\approx89.1$ years