The equation on number 3 is showing that Henry hikes 0.5 miles per hour, with x = number of hours. The graph shows that Clark hikes 15 miles in 10 hours, or 1.5 miles per hour. Clark is faster because of the reasons listed above.
Problem 4 is strange because it has a different value from x = 1 to x = 4 than it does for x = 5 and above, but my best guess would be a piecewise function:
If x < or equal to 4, 15x. If x > 4, 10 × (x - 4) + 60.
Problem 5 is much simpler: because x goes up 16 every time y goes up 6, 6/16 × x or (6/16)x.