Rosie needs to mow her lawn. She has just bought a new lawn mower, and believes she can mow at a rate of 2 m² a minute. With her old mower, she could only mow the lawn at a rate of 1 m² a minute. Her lawn is 10m by 25m. There is a patio in one corner which is 2m by 3 m and which she does not need to mow.