The length of a rectangle is twice the sum of the width and 18. Write an equation for the length, 𝑙, in terms of the width, 𝑤.
If the width of the rectangle is 𝑤, then the sum of the width and 18 is 𝑤 plus 18. We are told that the length is twice this sum. We need to multiply 𝑤 plus 18 by two. The length 𝑙 is therefore equal to two multiplied by 𝑤 plus 18. We could distribute the parentheses or expand the brackets here. We could multiply two by 𝑤 and two by 18. This means that 𝑙 is also equal to two 𝑤 plus 36. We could use either one of these equations to calculate the length when given the width or vice versa.