For the following production functions: calculate marginal product of labor (L), marginal product of capital (K), and the technical rate of substitution. Identify if the production function exhibits constant, increasing, or decreasing returns to scale:
1) y=2K+3L
2) y=K^1/2 L^1/3
3) y=3K^1/2 L^1/2
4) y=K^1/2 L^3/2