Area = length * width
Area = (n yds + 40 yds) * 30 yds
or
Area = (30 yds * n yards) + (30 yds * 40 yards)
This is if you add the area of the rides to the area of the arcade (the first parenthesis is the rides, the second is the arcade.)
Error// Error// Error// Error// Error// Error//
We can take prime numbers so they don't have a common factor other than 1.
3, and 5.
So we have to list the multiples to find the LCM
3: 3, 6, 9, 12,
15, 18
5: 5, 10,
15, 20, 25
15 is the LCM of 3 and 5
So, you can notice that if two numbers, lets call them a and b, have no common factor, then

is the LCM.
Hope that helped :)