What is the value of a for the following circle in general form?
x2 + y2 + ax+by+c=0

The difference of 2 numbers is 21 and the quotient of the equation is 4 then what are the two numbers?

Tyler enjoys the fish so much that after his birthday his family decides to take him to a famous aquarium a tank at the aquarium is similar to his tank with the scale factor of 8 how many times greater is the volume of the tank at the aquarium than the volume of tyler tank

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?