Step-by-step explanation:
(a + b + c)^2 = (a^2 + b^2 + c^2) + 2(ab + bc + ca).
Therefore 9^2 = (a^2 + b^2 + c^2) + 2(12).
a^2 + b^2 + c^2 = 81 - 24 = 57.
Please find attached photograph for your answer.
