Let Sam be (S+8) years while his sister is S years.
S(S+8) = 105
S^2+8S-105 = 0
(S+15)(S-7) = 0
Sam’s sister is 7 years and Sam is 15 years old.
It looks like you've got six numbers lined up there, every one of them is the same number, and you need to have them added up.
Well, you've got (-6) listed six ==> <em>TIMES</em> <== , so the situation is the same as if you just wrote
6 x (-6)
and that's just <em>-36 </em>.
1. x/9+10=11 (x=89)
2. 3x-5=-2 (x=1)
3. 2x+15=-23 (x=19)
4. 5x-4=16 (x=4)
5. -8x+9=-7 (x=2)
6. 10x-12=-28 (x=1.6)
7. 3x+7=52 (x=15)
8. 5x-11=19 (x=6)
9. 4x+13=-91 (x=-26)
10. 2x-7=43 (x=-19)
