Question

When the sum of a number and 3 is subtracted from 13 the result is 7

Answer 1

the sum of the number is 3. 7+3=10
13-10=3.

Answer 2

13 - (n + 3) = 7
13 - n - 3 = 7
10 - n = 7
10 - n - 7 = 0
3 - n = 0
n = 3