Answer
See below.
Work Step by Step
a) Our equation is: $320=760e^{-0.145h}\\\frac{320}{760}=\frac{8}{19}=e^{-0.145h}\\\ln{\frac{8}{19}}=-0.145h\\h=\ln{\frac{8}{19}}\frac{1}{-0.145}\approx5.97$
b) Our equation is: $667=760e^{-0.145h}\\\frac{667}{760}=e^{-0.145h}\\\ln{\frac{667}{760}}=-0.145h\\h=\ln{\frac{667}{760}}\frac{1}{-0.145}\approx0.9$
