x = amount invested in the CDs at 4%
well, we know that he invested already 62000 on some stocks, then he'll be investing "x" on CDs, so the total amount invested will be 62000 + x.
[tex]\bf \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}\hfill \stackrel{\textit{8\% of 62000}}{\left( \cfrac{8}{100} \right)62000}~\hfill \stackrel{\textit{4\% of "x"}}{\left( \cfrac{4}{100} \right)x}~\hfill \stackrel{\textit{5\% of 62000+x}}{\left( \cfrac{5}{100} \right)(62000+x)}[/tex]
[tex]\bf \stackrel{\textit{8\% of 62000}}{4960}+\stackrel{\textit{4\% of "x"}}{0.04x}~~=~~\stackrel{\textit{5\% return on the two investments}}{0.05(62000+x)} \\\\\\ 4960 + 0.04x = 3100+0.05x\implies 1860+0.04x=0.05x \\\\\\ 1860 = 0.01x\implies \cfrac{1860}{0.01}=x\implies 186000=x[/tex]
