Visna had 5 comic books. His brother gave him 4 more comic books. Visna bought some more comic books at the store. Now he has 15 comic books. How many comic books did Visna buy at the store?

The inside wheels of a car traveling on a circular path are rotating half as fast as the outside wheels. the front two wheels are six feet apart. what is the number of feet in the path traced by the inside front wheel in one trip around the circle? express your answer in the form "k \pi", where k is an integer.

9/10 divide by -3/15 as a mixed number

If y varies directly as x2 and y=6 when x=6, find the constant of variation.