Ok so we need to find out what fraction of 12 the veggies are. To do this we need to add the beef and chicken so
1/3 x 4 = 4/12 so we have a common denominator to add both fractions.
4/12 + 5/12 = 9/12
This means that 3/12 chose veggie
3/12 is equivalent to 1/4 (divide by three)
so if we multiple 69 by 4 we get the total number of guests.
69 x 4 = 276
I hope this helps