7a + 6c + 9a - 15c
-- Look for all the 'a's 7a, 9a
-- Addum up 16a
-- Look for all the 'c's 6c, -15c
-- Addum up -9c
-- Write the results 16a - 9c
I dont get what you asking
Next time use the desmos calculator online and input the numbers.
The answer to this equation is:
y = (x - 3)^2 - 2