The expression for the amount of money earned on a savings account compounded quarterly is given by the expression x(1.1)^4t, where x represents the principal and t is the time in years since the principal was invested. which expression is the equivalent form of the given expression and shows the amount earned when the interest is compounded half- yearly? a. x(1.4641)^t b. x(1.4641)^2t c. x(1.21)^t d. x(1.21)^2t