Please help me... :(

For parts 1 and 2, you'll need to find a way to gather these data points, either by measuring them yourself or by asking your friends. Another option is to search out "Census at School", with quotes, and it will lead you to spreadsheets of data on this sort of thing (that some researchers have already done previously).

In short, the answers to parts 1 and 2 will vary depending on what the actual data values you collect. So I'm not much help here in this case.

Part 3

Part A

In this case, we have x = 17 as the length of the person's forearm in inches. We'll plug it into the given regression equation to find an estimate of y

y = 0.860x + 3.302

y = 0.860*17 + 3.302

y = 14.62 + 3.302

y = 17.922

The person's foot is approximately 17.922 inches long

Rounding to the nearest whole number, this is approximately 18 inches

Note: 18 inches = 12 in + 6 in = 1 ft, 6 in = 1.5 ft

Part B

Unfortunately I can't help with this part either because I don't know what data set you're working with. So it all depends on how you do parts 1 and 2.  You shouldn't get the same exact values, but you should get close to the average.