4. Hong Securities has $300,000 to invest in four stocks and three bonds. X1, X2, X3, and X4 denote the amounts invested in each of the stocks, and Y1, Y2, and Y3 equal the amounts invested in each of the three bonds. Which of the following shows that at least 40% of the investment in stocks must be in stock 1? a) X1 >=120,000 b) X1 - .4X2 -.4X3 - .4X4 >=0 c) .6X1 - .4X2 - .4X3 - .4X4 >= 0 d) X1 >= .4(X2 + X3 + X4 + Y1 + Y2 + Y3)