We'll first clear a few points. 1. A hyperbola with horizontal axis and centred on origin (i.e. foci are centred on the x-axis) has equation x^2/a^2-y^2/b^2=1 (check: when y=0, x=+/- a, the vertices) The corresponding hyperbola with vertical axis centred on origin has equation y^2/a^2-x^2/b^2=1 (check: when x=0, y=+/- a, the vertices).
The co-vertex is the distance b in the above formula, such that the distance of the foci from the origin, c satisfies c^2=a^2+b^2. The rectangle with width a and height b has diagonals which are the asymptotes of the hyperbola.
We're given vertex = +/- 3, and covertex=+/- 5. And since vertices are situated at (3,0), and (-3,0), they are along the x-axis. So the equation must start with x^2/3^2.
It will be good practice for you to sketch all four hyperbolas given in the choices to fully understand the basics of a hyperbola.
Explaination: subtract 215 from 390 since thats how many the parts cost and we're trying to find how many hours the repair took.(answer 175) now divide that by 35 since thats how much you pay an hour. thats how many hours it took to repair the car