Step-by-step explanation:

Let's solve your equation step-by-step.

m2+21m+20=0

Step 1: Factor left side of equation.

(m+1)(m+20)=0

Step 2: Set factors equal to 0.

m+1=0 or m+20=0

m=−1 or m=−20

Answer:

m=−1 or m=−20