Business Maths question

a) find the amount that should be invested in order to earn $1950 over 5 years at a simple interest rate of 2.8% p.a?

b) How long would it take to the nearest year will it take $2000 to reach $3000 if it is invested at 7% p.a compounded monthly?

thanks please show working out

a) Let x = amount invested. The interest on x for 5 years is (2.8% X 5)x, or 0.14x
0.14x = $1,950
x = $1,950 / 0.14
x = $13,928,57

b) $3,000 / $2000 = 1.5
7% compounded monthly = 0.5833333% monthly, or 0.05833333

ln(1.5) = 0.405465108
ln(1.005833333) = 0.005816385

ln(1.5) / ln(1.005833333) = 69.7 months

72 months is 6 years, so 6 years is the correct answer.

initial amount = $1950 / (1.028)^5 = $1698.513637

3000/2000 = (1 + .07/12)^x (x is the number of MONTHS)
log(3/2) = x log(1 + 0.07/12)
x = log(3/2) / log(1 + 0.07/12) = 69.71084027 months
better round up to 70 months = 5 years 10 months