Question

D+d+d+d=120 what is d

Answer 1

The answer to D should be 30.

Answer 2

remember you can do anything to an equation as long as you do it to both sides

assumind D=d

d+d+d+d=120
4d=120
divide both sides by 4
4d/4=120/4
d(4/4)=30
d(1)=30
d=30

d=30