Your answer is A)(1,1) is the solution to both lines K and J
That's because the solution to a system of equations has to be the solution to both of the lines. Also, both of the lines intersect at the point (1,1).
Joe completes an average of (10 ft)/(5 h) = 2 ft/hour. Bill completes an average of (10 ft)/(4 h) = 2.5 ft/hour. Together, they complete 2+2.5 = 4.5 ft/hour. At that rate, it will take them