Terry takes typing. He can type 42 words per minute.
If he can improve 3 words
per minute (wpm) with 30
minutes' practice, how
many hours wili it be
before he can type 60
wpm?

How many triangles can be drawn with side lengths 4 centimeters, 4.5 centimeters, and 9 centimeters? explain

What is the difference between the predicted value and the actual value

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.