Answer:
-33+15n
Explanation:
You will have to first distribute the -3.
-3*4 is equal to -12
-3*-5b is equal to 15b Note: -*-=+
-3*7 is equal to -21
Once you get those numbers you will have a equation like this
-12+15b-21
Combine like terms and you will get -33+15n as you answer