when dividing 918 by 4.2, what number should the divisor be multiplied by in order to make it a whole number

To make 4.2 a whole number, we need to make the decimal places equal to zeros

4.2 = 4 + 0.2

Think of a number that multiplied by 0.2 gives a whole number. The smallest number possible will be 5 since 0.2 × 5 = 1

So we multiply 4.2 by 5

4.2 × 5 = [4 × 5] + [0.2 × 5] = 20 + 1 = 21

Applying this change into the whole sum

918 ÷ 4.2 
[918 ÷ 4.2] × 5 = [918 × 5] ÷ [4.2 × 5] = 4590 ÷ 21 

Now you have a sum whose terms in whole numbers only

It's like discovering the answer to a puzzle. the purpose in solving an equation is to find the value or values of the variable that makes it a true statement. any value of the variable that makes the equation true is called a solution to the equation.