Calculating the weights of each individual stock:

For stock-A: $400,000 / $4,000,000 = 0.1 or 10%

For stock-B: $600,000/ $4,000,000 = 0.15 or 15%

For stock-c: $1,000,000 / $4,000,000 = 0.25 or 25%

For stock-D: $2,000,000 / $4,000,000 = 0.5 or 50%

Calculating the portfolio beta :

Portfolio beta = W1 * Beta of stock-A + W2 * Beta of stock-B + W3 * Beta of stock-C + W4 * Beta of stock-D

= 0.1 * 1.50 + 0.15 * (0.50) + 0.25 * 1.25 + 0.5 * 0.75

= 0.15 - 0.075 + 0.3125 + 0.375

= 0.7625

Now, calculating the required rate of return:

E(Rp) = Rf + [Rm - Rf] * portfolio beta

= 0.06 + [0.14-0.06] * 0.7625

= 0.06 + 0.061

= 0.121 or 12.1%