Someone please explain how to answer

How to determine whether two known pairs of points are on the same line.

Twice the sum of a number and 4 is equal to three times the difference of the number and 7. find the number.

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.