Replace A,B,C with numbers so that:

Question

A*A=B
B-A=C
A+A=C

Answer 1

2nd: C = B-A
3rd: C = A+A
so B-A = 2A
B = 3A

In 1st:
A^2 = 3A
a^2 - 3A = 0
A(A-3) = 0
A = 0 or A = 3

if A=3, B = 9, C = 6
if A=0, B=0, C=0

Answer 2

A=3 B=6 C=9

Answer 3

A= 3
B= 9
C= 6