If we consider it as a combination problem, then we could calculate the how many combinations are there if we pick up three nodes out of six nodes, and then we have:

And the answer should be 20
Step-by-step explanation:
y=k/x
y=20, x=2
Substitute this first to get "k"
20=k/2
k=40
Value of y when x=10... is now
y= 40/10
y=4.
The tank hold 15 gallons.Because you divide 16.50 by 1.10 .