Factoring help? Easy grade 10

I have 2 questions: m²+5m=0
and d²-21d=0

Thanks & explain! :}

m(m+5) = 0
m+5=0/m
m+5 =0
m = - 5


d( d- 21) = 0
d -21 = 0
d = 21

For real this is 10th grade stuff? Where I`m at we get this in the 7th grade! Anyway, here`s the solution:

m1+m2=-5
m1*m2=0
m1=-5
m2=0

d1+d2=21
d1*d2=0
d1=21
d2=0

m(m+5)=0 m=0 or m+5=0
m=0 or m=-5
d(d-21)=0 d=0 or d-21=0
d=0 or d=21
if you multiply the number before the parantes you will get your first equation

m(m+5)=0 so either m=0 or m+5=0

solutions: m=0 and m=-5

d(d-21)=0, m=0 and m=21