I'm sorry if this questions sound stupid or something but I'm really interested in this.
I know how to graph some numbers and then find out values of some point in it, however I'm wondering if there is some mathematical formula that can help me to find that without drawing it.
Let's say I have some values like in the picture, I need to know value of
40%, is there any mathematical way of doing it? Any formula for it so I can, maybe write computer program that does this for me?