Answer:
Ok, Diego has 500 dollars in his savings account. Each month he will take out 20 dollars to pay for karate classes. Basically your trying to find how many cash will you have left after paying $20 each month. In a year there are 12 Months. Equation to find how much do you pay in a year.
Equation: $20 x 12 months = total amount of dollar needing to pay for karate classes.
20 x 12= $240 for a year so that will leave Diego at the end of the year with $260 in his savings account.
Hope this helps.