So the formula is
7*(1/3+1/5) = x
First find the common denominator of the fractions. In this case the common denominator of 3 and 5 is 15 so we must convert them to 15ths. To do that we divide 15 by the denominator and take that answer and multiply the numerator by it.
So for 1/3 we take 15/3(denominator) = 5 and multiply the numerator (1) by it
5 * 1 = 5 so 1/3 converts to 5/15
Do the same for 1/5 we take 15/5 = 3 and multiply the numerator (4) by it
3*4 = 12 so 4/5 converts to 12/15
Now we add 5/15 and 12/15 = 17/15 so we have our formula now to
7*17/15
We make seven a fraction 7/1 and multiply across 7*17 = 119 and 15 * 1 = 15
We have 119/15 which when we divide and get 7 14/15 as your answer