What's the answer to these questions? how did you solve them?

Which matrix multiplication is possible?

Twenty points. suppose that one doll house uses the 1 inch scale, meaning that 1 inch on the doll house corresponds to 1/2 foot for life-sized objects. if the doll house is 108 inches wide, what is the width of the full-sized house that it's modeled after? in inches and feet

The ph level of a blueberry is 3.1 what is the hydrogen-ion concentration [h+] for the blueberry