Answer:
x = 18 minutes.
Step-by-step explanation:
We work in fraction of the work done per minute.
You rake 1/30th of the yard in 1 minute and your brother rakes 1/45 of the yard in 1 minute. So we have:
1/30 + 1 /45 = 1/ x where x = time taken when working together.
Multiply through by the LCD ( = 90x):
3x + 2x = 90
5x = 90
x = 18 minutes.