Answer
Find out the what fraction of the sandcastle did they build together .
To prove
Let us assume that the fraction of the sandcastle they build together be x .
As given


Than the equation becomes

L.C .M of (3,7) = 21
solving


Therefore the fraction of the sandcastle did they build together be

Hence proved
Answer:
true
Step-by-step explanation:
direct proportion y=kx , k is constant and k does not equal to 0.
17.5=k(21)
k=5/6
when x =39
y=5/6 ×39
y=32.5
The LCM of 15 and 6 is 30
5x6
12x2