If you would like to write the following in the math expression, you can do this using these steps:
a number ... n
twenty less than 8 times a number ... 8 * n - 20
is the same as ... =
15 more than the number ... n + 15
8 * n - 20 = n + 15
8 * n - n = 15 + 20
7 * n = 35 /7
n = 35 / 7
n = 5
The number we are looking for would be 5.