Question

Can someone please explain how to do this? I don’t need the answer I just don’t know how to solve it.

Answer 1

Let $P$ be the number of plain cakes sold, and $D$ the number of decorated cakes sold.

Each plain cake sells for $7, so $P$ cakes sells for $\ 7P$.

Similarly, each decorated cakes goes for $11, so $D$ cakes are worth $\ 11D$.

The baker sells all but 3 cakes, so

$P + D = 117$

After the sale, the baker earns a total of $991, so

$7P + 11D = 991$

Now just solve the system of equations for $P$ and $D$. This is easily done by substitution or elimination.

(The selected answer is actually the correct one.)