Explanation

This solves a rectangle from its perimeter and area. Perimeter 10 gives l + w = 5; area 4 gives lw = 4. So l and w are the roots of t² - 5t + 4 = 0, i.e. {4, 1}. The length (the longer side) is 4 cm. Option (b) 5 cm is the trap — it is the semi-perimeter, not a side. Hence option (d).