Let x be the number.
15 more than a square of a number is:
Eight times the number is:
8*x or 8x
The identifier "is" on the question means the two are equal, therefore, we make an equation:
Transferring 8x to the left hand side, we get:
We did this step because it is easier to find the roots in this form.
x-5=0 , therefore x=5 ||| x-3=0, therefore x=3
So we have two solutions.
Let's check if they're both correct. We will substitute the values that we got on the first equation we did.
If x is 5:
The solution x=5 is correct.
The solution x=3 is also correct.
Hope that helps.