It's not entirely clear due to lack of parenthesis, but I think your function has 20 all over the quantity 1+9e^(3x)
If so, then you should write it as such: 20/( 1+9e^(3x) )
Let's plug in x = 0 and see what the function output is
y = 20/( 1 + 9e^(3x) )
y = 20/( 1 + 9e^(3*0) ) ... replace every x with 0
y = 20/( 1 + 9e^(0) )
y = 20/( 1 + 9(1) )
y = 20/(1+9)
y = 20/10
y = 2
Therefore the y intercept is 2 meaning that the graph crosses the y axis at the location (0,2). The y intercept is always where x = 0. Since 0 is a good starting point, the y intercept is often used as a starting value.
