Can someone help me with this please

The multiplication property of zero states that the product of any number and 0 is 0. what must be true about either a or b to make ab=0

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Which situation can be modeled by the inequality 5 + 10w ≥ 45? a. you start with $5 and save $10 a week until you have at least $45. b. you start with 5 baseball cards and purchase 10 cards every week until you have at most 45 cards. c. you start with 5 water bottles and purchases cases of 10 water bottles each until you have a total of 45 water bottles. d. you spend $5 plus $10 per week until you have less than $45.