Complete the solution of the equation. find the value of y when x equals 15. 3x ‒ 8y = 5 y= ?

So first, we want to substitute in 15 to all the x variables.

So,

3x - 8y = 5

Becomes

3 * 15 - 8y = 5

Or, 

45 - 8y = 5

So here, you can subtract 45 from both sides to move all like terms to one side.

-8y = 5 - 45

And then simplify:

-8y = -40

Then divide both sides by -8

y = 5

Understanding what? lol