Computing $E(X)$ of continuous PDF using geometry (as opposed to calculus)

Question: https://brilliant.org/practice/distributions/?problem=probability-problem-162854&chapter=intro-to-random-variables-distributions

I understand the Calculus (as far as integration is concerned) but I am failing visualizing it geometrically.
Quoting the explanation:

Given that PDF is bounded by x=1/5, x=0, y=-2 and y=3:

How come the height of triangle on left side of x=0 is 2/5?

Or why is the height of triangle on right of x=0 is 3/5?

#Combinatorics

Easy Math Editor

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Math	Appears as
Remember to wrap math in `$` ... `$` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

We want to find the difference in areas between the two triangles formed.

I will request the author of this quiz to add a suitable image in that explanation.

In the future, if you have concerns about a problem's wording/clarity/etc., you can report the problem. See how here.

Brilliant Mathematics Staff - 3 months ago

Thanks for reply. I think my lack of understanding is probably a bigger issue here than problem's wording. I see what I was getting wrong. E(x) = Integration of (x f(x)) I was a taking area under the graph of rectangle (what PDF is) instead. Thanks for clarification!

shanxS Phone - 3 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Computing E(X) E(X)E(X) of continuous PDF using geometry (as opposed to calculus)

Comments

Computing $E(X)$ of continuous PDF using geometry (as opposed to calculus)