So you need to get to 29 lawns right? So 29 is a prime number and doesn't have three as a common factor. So you have to get down to the very last bit on how often he mows lawns in the seven months. 7/3 does that, it's not precise but it's a great estimation.
2.333=7/3
So every 2.33... months he mows a lawn. So what's 3's closest factor to 29? 27. So now do 7*9 as in the months and stuff. You get 27, already 27 months off the bat. Now then do 2.33...*2=4.66 months extra.
Here it is, just in case you don't want to read this all.
7/3=2.33...
7*9=27
29-27=2 2*2.33...=4.66+27
31.66 more months
