Ok so,
Let's substitute the ? For y.
X + y= 90 degrees
Y= 2x-3
So x + 2x-3=90 using the substitution property.
Then you need to solve for x which leaves you with x=31.
But that's not the final step.
You're not solving for x you are solving for the y or in this case the ?.
After that you can either subtract 31 from 90 or multiply 31 times 2 and subtract three.
Either way you end up with 59.