Answer:
17*21 = 357
Step-by-step explanation:
Firstly, set up your equation.
x*(x+4)=357
Multiply X by (x+4)
x^2+4x=357
You then subtract 357 from both sides
x^2+4x-357=0
Simplify using the quadratic formula shown, if you need assistance on solving this equation put it into a online calculator, or photomath as it shows the steps taken to solve it.
[tex]\frac{-4+\sqrt{4^2-4\cdot \:1\cdot \left(-357\right)}}{2\cdot \:1}\\[/tex]
