0=x^2-20 can you solve using square root formula? then by using quadratic formula?

Acomputer store bought a program at a cost of $10 and sold it for $13. find the percent markup

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

Taber invested money in an account where interest is compounded every year. he made no withdrawals or deposits. the function a(t)=525(1+0.05)^t represent the amount of money in the account after t years. how much money did taber origanally invested?