c = cost of food/med for cats
d = cost of food/med for dog
y = total cost/spent
What you know:
y = 6c + d [has 6 cats and 1 dog]
c = 2/3d - 5 [cost for cat is 5 less than 2/3 cost for dog]
y = $195
y = 6c + d
Substitute/plug in what you know, plug in (2/3d - 5) for c and 195 for y
195 = 6(2/3d - 5) + d Distribute/multiply 6 into (2/3d - 5)
195 = 4d - 30 + d Combine like terms
195 = 5d - 30 Add 30 on both sides of the equation
225 = 5d Divide 5 on both sides
$45 = d
