The formula for the balance of an account with principal P, an annual interest rate of r (expressed as a decimal), compounded n times per year, for t years, with no additional deposits or withdrawals, is:
A = P * (1 + r/n)^(n*t)
In this case, "Rosario" invests $2000 in an account that earns 3.5% interest compounded quarterly, which means that n = 4 (since there are 4 quarters in a year) and r = 0.035 (since 3.5% is 0.035 expressed as a decimal). Therefore, the equation for the balance of the account A after t years is:
A = $2000 * (1 + 0.035/4)^(4*t)
Simplifying this equation, we get:
A = $2000 * (1.00875)^(4*t)
Therefore, the balance of "Rosario's" account after t years is given by the equation A = $2000 * (1.00875)^(4*t), where t is the number of years the money has been invested.