Missing Side of Rectangles – Perimeter Practice Worksheets Help your students master 3.MD.8 with this no-prep worksheet set! Students practice finding the missing side length of rectangles when given the perimeter and one side. Students will use division and subtraction to determine the unknown side and build confidence with multi-step problem solving. What’s Included: 20 practice problems per worksheet Multiple worksheet versions for repeated practice Missing side answers are 12 units or les