4 bags of cement do 18m2 how many m2 can be done with 7 bags

We will represent the word bags with the letter b and the unknown with x

4b = 18m²

7b = xm²

To work this out, we will first have to work out how many m² one bag will cover.

We know that 4b = 18m²

To get from 4b to b, we must divide by 4

Therefore to get from 18 to the missing value, we must divide by 4

18/4 = 4.5m²

Now we must work out how to get from 1 bag to 7 bags

We multiply by 7

Therefore we do the same to 4.5m²

4.5 x 7 = 31.5m²