Answer:
y=(x+4)^2 -37
Step-by-step explanation:
y+ ? = x^2 +8x+ ?-21
y+? =x^2+8x +16-21
y+16=x^2+8x+16-21
y+16=(x+4)^2 -21
y=(x+4)^2-21-16
Calculate the difference
