Write an equation that has variables on both sides and has a solution of -3

Here's an example (which I'll walk you through):

2x + 5 = -1 - x

This has variables on both sides (because there's an x on the left side of the equals sign, and on the right side).

And the solution is also -3. Here's how:

2x + 5 = -1 - x

First, I'll move the x on the right side to the left by adding x to both sides:

2x + 5 + x = -1 - x + x

This cancels out the -x on the right and adds another x to the 2x on the left:

3x + 5 = -1

Now to isolate the 3x, I'll subtract 5 from both sides:

3x + 5 - 5 = -1 - 5

This cancels out the 5 on the left side, and subtracts 5 from the -1 on the right:

3x = -6

Now I'll divide both sides by 3 to get x on its own and find my solution:

3x ÷ 3 = -6 ÷ 3

This cancels out the 3 multiplying the x on the left, and it divides the -6 by 3.

x = -2

And there's your solution :)

the revenue of the fitness center, y, is the product of two factors: the number of members and the fee paid by each member. there are 320 members now, but number of members goes down by 10 for each $5 increase in fees, so if x is the number of $5 price increases then members is equal to (320 - 10x). since the fee is currently $45, and the fee increases by $5 for every price bump x, the fee is given by (45 + 5x). so, revenue y is given by y = (320 - 10x)(45 + 5x).