Y = k/x is the inverse equation.
6 = k/11
Solving for k, multiply by 11 on both sides.
66 = k
y = 66/x
13.2 = 66/x
x = 5
This I think could be technically answered in a couple of ways. Fill the 4 gallon bucket up and then fill the 7 gallon bucket up 1/7 of the way. Or fill the 4 gallon bucket up and transfer to the 7 gallon bucket and fill the 4 gallon bucket up 1/4 of the way. Either way the 1/4 or the 1/7 will be a close estimate to get your 5 gallon bucket. I hope this helps.
-50 and -18 multiplied together equal 900 and added together equal -68 because a - times a- equals a positive.