Anybody wanna explain this

Uanita borrowed $600 to purchase a new computer. she was charged 7% interest for two years. she used the simple interest formula to find the interest. i = 600(7)(2) what error did juanita make and how will her error affect the interest she calculates? explain.

If a • b*2 = 1.8 x 10*-7, and c•b/d = 7.2 x 10*-4, find the value of a•d*2/c*2

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.