David scored x marks for his mathematics test, edwin scored 4/5 of what david scored. frank scored 38 marks more than edwin and gabriel scored 5 fewer marks than frank.
(a) express gabriel's marks in terms of x.
(b) if the average mark of the four boys is 64.5, find gabriel's marks for the mathematics test.

Find an equation for the linear function which has slope -10 and x-intercept -7

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters

Find the volume of the solid obtained by rotating the region enclosed by the curves y=1x and y=7^-x about the x-axis. (use symbolic notation and fractions where needed.) volume =