From the following figure, how to obtain an aggregate demand function?

The correct answer is Option (4) → OL

The Aggregate Demand function shows the total demand (made up of consumption + investment) at each level of income. Graphically it means the aggregate demand function can be obtained by vertically adding the consumption and investment function.

Here, OM = $\bar C$

OJ = $\bar I$

OL = $\bar C$ + $\bar I$

The aggregate demand function is parallel to the consumption function i.e., they have the same slope c.