So, we need to gain at least 9.99$ from the interest rate. Hence, if we store x, we will gain x*0.02% and thus x*0.02%>9.99 must hold. We need to convert the percentage to a decimal: 0.02%=0.02/100=0.0002. Then, we have that x>9.99/0.0002. Doing the calculation, we have that x>49950$. This value is the least value that covers our fee exactly.
