I am having troubles finding x, need an explanation

When drawing a trend line for a series of data on a scatter plot, which of the following is true? a. there should be an equal number of data points on either side of the trend line. b. all the data points should lie on one side of the trend line. c. the trend line should not intersect any data point on the plot. d. the trend line must connect each data point on the plot.

What is the value of x in the diagram below?

Which expression is equivalent to 8(k + m) − 15(2k + 5m)?