Ellen is playing a video game in which she captures butterflies. there are 3 butterflies onscreen, but the number of butterflies doubles every minute. after 4 minutes, she was able to capture 7 butterflies.

a. look for a pattern write an expression for the number of butterflies after 4 minutes. use the power of 2 in your answer

b. write an expression for the number of butterflies remaining after ellen captured the 7 butterflies. simplify the expression