On the problem of solving the sixth grade of primary school mathematics. There must be a process.

①、6:x=36:72

Solution: x=72×6÷36

x= 12

②、2/7=5/x

Solution: 2x=7×5

x= 17.5

③、x:2/5= 15:5/8

Solution: x=2/5× 15÷5/8.

x=9.6

④、 1.2:0.3=0.8:x

Solution: x=0.3×0.8÷ 1.2.

x=0.2

The ratio of 85 to x is equal to the ratio of 18 and 12. Formula: 85: x = 18: 12.

The ratio of x to 4/5 is equal to 1/4 and 3/4. Formula: x: 4/5 = 1/4: 3/4.

The two internal terms of bile are 16 and 24 respectively, and the two external terms are x and 48 respectively. Formula: x: 16=24:48.

The left end of the equal sign is 1.2: x, and the ratio of the right end of the equal sign is 2.4 and 3.6 respectively. Formula: 1.2: x = 2.4: 3.6.