Answer
$ 7\%$
Work Step by Step
The bond costs (now) $PV$=$10,000$
Using the simple interest formula,\ the total interest
over a period of t=$4$ years
is
INT=$PV\cdot rt$
solving for r, (divide with $PV\cdot t$)
$r=\displaystyle \frac{INT}{PV\cdot t}=\frac{2800}{10,000\cdot 4}= 0.07$
