I believe that 15x is trying tell you to do 15 minus -10 15 times maybe?
Steps°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Simplifying
15x = 125
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Solving
15x = 125
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Solving for variable 'x'.
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Move all terms containing x to the left, all other terms to the right.
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Divide each side by '15'.
x = 8.333333333
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Simplifying
x = 8.333333333
°.✩┈┈┈┈∘*┈┈୨♡୧┈┈*∘┈┈┈┈✩.°
Hope this helps!