Laura buys 3 packs of inventions.
20-11=9
(amount given-change=actual cost)
9 ÷ 3 = 3
(actual cost ÷ dollars per pack= number of packs bought)
Let EB and CF be two heights. Then quadrilateral EBCF is rectangle, so BC=EF=5 m. It is given that bases are BC=5 m and AD=11 m. Triangles ABE and DCF are congruent, thus,

Consider right triangle ABE, by the Pythagorean theorem

Answer: 
The answer should be $60 per minute