The given equation, V = 4 + 2t, is a linear function, which means that its graph is a line.
The slope of such graph is constant; it is the coefficient of the independent variable (t in this case) and the constant term (4 in this case) is the initial value of the function (when t = 0).
To graph such function you follow these steps:
Draw two perpendicular axis: the horizontal and the verical axis.
Label the horizontall axis with the name and units of the independent variable: time in minutes.
Label the vertical axis with the name and units of the dependent variable: volmen of water (the units are not stated, so you cannot add this important information on your graph)
Choose an adequate scale and do marks on every axis: in this case I will do marks of 1 unit each.
Mark the initial value, i.e. the volume when t = 0, which is: V = 4 + 2t = 4 + 2(0) = 4 + 0 = 4
Mark other point. For example, t = 4 ⇒ V = 4 + 2(4) = 4 + 8 = 12
You can check that the slope is equl to rise / run = 2, and the y-intercept is V = 4.
Finally, do not forget to add the title of the graph: volume of water in a bucket