For the following production function, please do the following:

Y = aK + bL; a,b > 0

Part A [5 points]. Find whether they have increasing, constant, or decreasing Returns To Scale;

Part B [5 points]. Draw the isoquant map for two or more levels of output;

Part C [5 points]. Derive the marginal rate of substitution of K for L;

Part D [5 points]. Comment on the realism of the functional form for a trucking industry.