X:30=7 420:x=60 z+250=900

Question

X:30=7
420:x=60
z+250=900

Answer 1

1)x=210
2)x=25200
3)x=650

Answer 2

X:30=7.
x=7*30
x=210
420:x=60
x=420:60
x=7

z+250=900
z=900-250
z=650