Why is it important to define a variable before writing an equation?

What is the measure of sty in oo below? 130 310 230 50

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

Anew landowner is interested in constructing a fence around the perimeter of her property. her property is 1,080√30 feet wide and 500√20 feet long. what is the perimeter of the property? (recall that the perimeter is the sum of each side of a shape or boundary). a 1,580√40 feet b. 5,320√5 feet c. 3,160√20 feet d. 10,640√5 feet