If one us dollar equals .5 british pounds, you would receive british pounds if you exchanged $15.

To find the number of British pounds you will receive in exchange for $15, you will multiple the number of groups of dollars by 0.5 British pounds because this is how many groups of 0.5 you will receive.

15 x 0.5 = 7.5

You will receive 7.5 British pounds.