Answer:
k = 27/4
y = 283.5
Explanation:
Let
y = amount of water used
x = number of dogs washed
y = kx
y = 81 gallons
x = 12 dogs
y = kx
81 = k * 12
81 = 12k
Divide both sides by 12
81/12 = 12k/12
k = 81/12
k = 27/4
k = 6.75
Find x when y = 42 dogs
y = kx
y = 27/4 * 42
y = (27*42) / 4
y = 1,134 / 4
y = 283.5
y = amount of water used = 283.5 gallons