Prove that if ab= 0and a is invertible then b= 0

Adeli owner keeps track of the to-go orders each day. the results from last saturday are shown in the given two-way frequency table. saturday's to-go deli orders in person by phone online total pick up 38 25 31 94 delivery 35 28 34 97 total 73 53 65 191 what percent of the to-go orders were delivery orders placed by phone? a. 14.66% b. 38.41% c. 28.87% d. 52.83%