Respuesta :
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
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