Answer:
3/5 hours or 36 minutes
Explanation:
John could mow three of these lawns in three hours (3/1 = three), while Sam could only mow two in three hours (3/1.5 = two). Therefore, the two of them could cut 5 lawns in 3 hours (3+2). Together, they can cut the same lawn in three and a half hours, or 36 minutes.