1200(1.03^x) = 800(1.08^x)
divide by 800 on both sides
divide by 1.03^x on both sides
1200/800 = (1.08^x)/(1.03^x)
3/2 = (1.08/1.03)^x
ln(3/2) = ln( (1.08/1.03)^x )
ln(3/2) = x * ln(1.08/1.03)
Exact: x = ln(3/2) / ln(1.08/1.03)
Decimal, approximate: x = about 8.554