Question

Subtract:
(-3a+6b-c)-(-3b+2c-7d)=

Answer 1

First remove the brackets to give:
-3a + 6b -c +3b -2c + 7d
Do you follow this step?

Answer 2

Then you add like terms giving:
-3a +9b - 3c +7d as the answer

Answer 3

-3a+9b-3c+7d as done by kropot72