The work done by a body on application of a constant force is the product of the constant force and the distance travelled by the body in the direction of force. Express this in the form of a linear equation in two variables and draw its graph by taking the constant force as $3$ units. What is the work done when the distance travelled is $2$ units? Verify it by plotting the graph.

(N/A) Work done $= (\text{constant force}) \times (\text{distance})$
$= 3 \times (\text{distance})$
i.e., $y = 3x$, where $y$ (units) is the work done and $x$ (units) is the distance travelled.
Since $x = 2$ units (given), therefore, work done $= 3 \times 2 = 6$ units.
To plot the graph of the linear equation $y = 3x$, we need at least two solutions of the equation.
We see that $x = 0, y = 0$ satisfies the given equation, and $x = 1, y = 3$ also satisfies the equation.
Now we plot the points $A(0, 0)$ and $B(1, 3)$ and join them to form a line. The graph of the equation is a straight line. [We have not shown the whole line because work done cannot be negative].
To verify from the graph, draw a perpendicular to the $x$-axis at the point $(2, 0)$ meeting the graph at the point $C$. Clearly, the coordinates of $C$ are $(2, 6)$. It means that the work done is $6$ units.