what formula do i have to use for this problems.

Problem #4
John Lee saving account has a balance of $2449.After 7years what will be the amount of interest be at 8% compounded semiannually?

Problem #5
Southewest Dry cleaners believes that it will need new equipment in 5 years the equipment will cost $26,000 what lump sum should be invested today at 8% compounded semiannually to yield $26,000?

4. $2449 x (1.04)^14 = $4240.88
(The account is increased by 8%/2 = 4%, 7X2 = 14 times)

5. X * (1.04)^10 = $26,000.
Solve for X

what are the names of the formulas you used for them....

also for #5 i tryied solving for x i ended up with 25998.5976