Find the number of bicycles and tricycles Help for my son.  My math is a bit rusty and I'm trying to remember how to go about answering this question:  "There are 3 times as many bicycles in the playground as there are tricycles.  There is a total of 81 wheels.  What is the total number of bicycles and tricycles in the playground?"     

\begin{align}
&\text{Number of bicycles} =3 \times 2x\text{ wheels}\\
&\text{Number of tricycles} =3x\text{ wheels}\\
&3 \times 2x\text{ wheels}\ +\ 3x\text{ wheels}=81\text{ wheels}\\
&9x=81\\
&x=9\\
&\text{Number of bicycles} =3 \times 9\\
&\text{Number of tricycles} =9\\
\end{align}
