Let
be the number of plain cakes sold, and
the number of decorated cakes sold.
Each plain cake sells for $7, so
cakes sells for
.
Similarly, each decorated cakes goes for $11, so
cakes are worth
.
The baker sells all but 3 cakes, so
After the sale, the baker earns a total of $991, so
Now just solve the system of equations for
and
. This is easily done by substitution or elimination.
(The selected answer is actually the correct one.)