Помогите решить(5м2 18дм2+82дм2)*84 , (52м2 - 279дм2)*902

1) 7/7=490

1/7=70

2/7=140

2)900=100%

900*15%/100%=13500/100%=135

15%=135

3) x=100%

   56=14%

14x=5600

x=400

4)8/10=640

  1=x

8/10x=640

x=800