Toby buys a new mp3 player for a price of $45.50. what is the total amount his credit card is charged if the sales tax is 7%

$45.50 x 1.07 = total
the subtotal is 45.50 x 1.00, the tax is 0.07x45.50.  Add these two together and you get the total. You can simplify this from two calculations and an addition to one calculation by adding the 1.00 and the 0.07.  think 2x + 1x = y, you can add your x's to get 3x = y.

Letter a i would say