How can you find the sales tax for a purchase ? explain

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

If a 36 inch yardstick casts a 21 foot shadow, how tall is a building whose shadow is 168 feet? what is the scale factor

What is the volume of a rectangular crate that has dimensions 9 inches by 9 inches by 1 feet? 1,458 in.3 121.5 in.3 1,012.5 in.3 36 in.3