to find the area of a rectangle, you multiply the length and width together. in this question, they give you the area and the length so you have to find the width. just divide it to find it.
A = l × w
347.13 = 20.3 × w
347.13 ÷ 20.3 = w
17.1 = w
the width is 17.1
hope this helps, God bless!