Answer
Find out the how much people were at the wedding.
To prove
Let us assume that the people were at the wedding be x .
As given
Joy organised a large wedding .
Guests had to choose their meals from beaf ,chicken or vegetarian .
69 people chose vegetarian .
Than the equation becomes
L.C.M of (3,12) = 12
than
12x = 69 × 12 + 4x + 5x
12x - 9x = 828
3x = 828
x = 276
Therefore 276 people were at the wedding.