Finding the y-intercept of a function

Finding the y-intercept of a function is easy if you are given the graph, but how do you find it if you are given only a function in a single variable?

Some images made using Geogebra.

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0:00 Introduction
0:08 Finding the y-intercept when given the graph
1:40 Steps to find the y-intercept of a function
2:45 What? No unnecessary math outro?