Verified Answer :

You can use cross-products to solve this problem. For instance, this expression would be written as 5(8)= 7(-x), or 40= -7x. What you'd do then is simplify the expression by dividing both sides of the equation by the coefficient of x, such that you'd isolate x and have the value of x.

5/7 = -x/8

First: What you would do is cross multiply. You would multiply 7 and -x, then 8 and 5.
Your equation should then look like: 40= -7x
Next: You would divide each side by -7 so you can get your x alone.
You would get: x= -5.71... < That would be your answer 

HOPE THIS HELPS! ^_^