Answer:
$70.47
Explanation:
Since the cost of the aquarium with the 15% discount is $59.90 then $59.90 is 85% of the original price. Remember 100-15=785. To find the original price set up a proportion with these values:

Solve for the original price by cross multiplying numerator with denominator.
x(85) = 59.90(100)
85x = 5990
x= $70.47