The other tutor interpreted "the difference between 10 and 5" as
simply 10-5. I'm quite sure that's not the way you were supposed
to interpret it. So I'm quite sure -8 is NOT the correct solution.
Here is the correct way to interpret it:
four times the sum of -2 and a number yields the difference between 10 and 5 times the number.
Change "a number" and "the number to N:
four times the sum of -2 and N yields the difference between 10 and 5 times N.
Change "the sum of -2 and N" to (-2+N)
four times (-2+N) yields the difference between 10 and 5 times N.
Change "5 times N" to 5N
four times (-2+N) yields the difference between 10 and 5N.
Change "four times (-2+N)" to 4(-2+N)
4(-2+N) yields the difference between 10 and 5N.
Change "the difference between 10 and 5N" to 10-5N
4(-2+N) yields 10-5N
Change "yields" to an equal sign
4(-2+N) = 10-5N
Now you can finish by yourself.
Edwin