need quick help! i dont understand these at all and i have a test tomorrow. damn summer school. anyways

A tourist walks n km at 4 km/h and then travels 2n km at 36 km/h by bus. Express the total traveling time t in hours as a function of n.

Answer is t(n) = 11n/36 i dont know how to get it though

A light 3m above the ground causes a boy 1.8m tall to cast a shadow s meteres long measured along the ground. express s as a function of d, the boy's distance in meters from the light. s(d) = 1.5d is the answer

Express the area A of a 30-60-90 right triangle as a function of the length of hypotenuse, h. answer is a(h)=h2root3/8