math question please

Question

a coin was sold for $266 in 1975 and was sold again in 1985 for $472. find the value of k of the exponential growth rate assume V=266

Answer 1

A=Ve^kt k=r=rate of interest, t years =10

472 = 266e^10r

236/133 = e^10r

ln(236/133) = 10r

r = ln(236/133)/10

r = about 0.0573= 5.73% = interest rate