Amanda's garden is rectangular and measures 12.5m by 9.2m. The garden is to be sown with grass seed. The gardener needs 25 kg of grass seed for each square metre of ground. Grass seed costs £5.35 per kg. The gardener estimates that he will need £20 to buy the grass seed. Amanda disagrees with the gardener's estimate. She gives the gardener £15 to buy the grass seeds. Which estimate do you agree with? Explain your answer.