Answer
They would need to invest an extra 55 thousand dollars ($55,000).
Work Step by Step
We assign the variable:
$x$ = extra money to be invested
Step 1: Find the equation that represents the problem.
We can get the equation from the wording in the problem.
From "Jeff invested $\$30,000$ and Kris invested $\$40,000$" and "to generate a total that will yield $\$6250$ annually with a 5% rate of return", we get:
$5\% * $ (initial investments by both Jeff and Kris + extra money invested) $= 6250$
$(30000+40000+x)0.05=6250$
Step 2:
Solve for $x$.
$(70000+x)0.05=6250$
$70000+x=\frac{6250}{0.05}$
$70000+x=125000$
$x=125000-70000$
$x=55000$
Step 3:
They would need to invest an extra $55$ thousand dollars.
