Two blocks are placed on the beam. Each box is $3$ metres long, $1$ metre high, and applies $21N$ of downward

force in total. The first box is placed directly on the beam flush with the left hand side of the beam. The

second box is placed on top of the first box, but is flush with the right hand side of the beam.

The beam and blocks look like:

Find an equation f$($x$)$ to describe the load distribution on the beam.