let's say the amounts are "a" and "b"
6% 4%
now... we dunno what "a" is, but nevermind, whatever that is, "b" invested at 4%, is 1600 less than that or less than "a", namely b = a - 1600
so.. "a" is the bigger amount than "b" by 1600, but no matter
what is 6% of a? well, 6/100 a or 0.06a, that's how much it yielded
what is 4% of b? well, 4/100 b, or 0.04b, that's much it earned in interests
we know, their yield, or total in earned interest is 156, so.. whatever those yields are, they add up to 156 or
0.06a + 0.04b = 156
now \(\bf \begin{cases}
\boxed{b}=a-1600\\\\
0.06a+0.04b=156\\
----------\\
0.06a+0.04\left( \boxed{a-1600} \right)=156
\end{cases}\)
solve for "a", to see how much was invested at 6%
how much is "b"? well, b = a - 1600
