Question 872269
x^2+8x-5=15


x^2+8x-5+5=15+5


x^2 + 8x = 20


x^2 + 8x + 16 = 20 + 16 ... take half of 8, then square it, add it to both sides


x^2 + 8x + 16 = 36



I'll let you finish up