How do you know if fractions are equal? ?

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

The area of each triangle is 7 square units. the surface area of the triangular prism is

The salesperson earns a 5% commission on the first $5,000 she has in sales. the salesperson earns a 7.5% commission on the amount of her sales that are greater than $5,000. this month the sales person had $8,000 in sales. what amount of commission, in dollars, did she earn?