You put $2000 into a college savings account that pays interest at an annual rate of 4%. if you make no additional deposits or withdrawals from the account answer the following questions.
how much will be in the account after 3 years?
how much will be in the account after 3 years compounded weekly?
how many years will it take for the account to contain $2500?
how many years will it take for the account to contain $3000?

Total = principal * (1 +rate)^years
Total = 2,000 * (1.04)^3
Total = 2,249.73

Compounded Weekly
Total = principal * (1 +(rate/52))^years*52
Total = 2,000 * (1.000769230769230769)^3*52
Total = 2,254.89

$2,000 4% compounded annually
When will it reach $2,500?
Years = {log(total) -log(Principal)} ÷ log(1 + rate)

Years = [ log(2500) - log(2000) ] / log (1+ .04)

Years = [ 3.3979400087 - 3.3010299957 ] / 0.0170333393

Years = 5.6894312564 (about 5.69 rounded)

$2,000 4% compounded annually
When will it reach $3,000?
Years = {log(total) -log(Principal)} ÷ log(1 + rate)
Years = [ log(3000) - log (2,000) ] / log (1.04)

Years = [  3.4771212547 -  3.3010299957 ] /  0.0170333393

Years = 0.176091259 / 0.0170333393

Years = 10.3380350675 (about 10.34 Years rounded)

Here's a calculator to double-check the work: http://www.1728.org/compint.htm

The answer is D) (-1,0) and (0,6). when you solve by substitution, all you need to do is solve for the variable in one equation and plug the answer into the other equation.