An investor has decided to invest at most $$100,000$ in securities in the form of corporate stocks.

He has classified his options into three groups: blue$-$chip stocks that he assumes will yield a $10\%$ return $($dividends and capital appreciation$)$ within a year, growth stocks that he assumes will yield a $15\%$ return within a year, and speculative stocks that he assumes will yield a $20\%$ return $($mainly due to capital appreciation$)$ within a year. Because of the relative risks involved in his investment, he has further decided that no more than $30\%$ of his investment should pe in growth and speculative stocks and at least $50\%$ of his investment should be in blue$-$chip and speculative stocks. Determine how much should be invested in each group of stocks in the hope of maximizing the return on the investments.

a$.$ Suppose the growth stocks are anticipated to yield a $12\%$ return instead of $15\%.$ Use a i just need help with solver the objective formula, I put D$5$ but it not working