First, notice that this equation is written in slope-intercept form which is more commonly known as y = mx + b form where the multiplier, m, or the coefficient of the ex term represents the slope of the line and the b or the constant term represents the y-intercept of the line.
I have attached slope-intercept form below.
Notice that below, the b is in place of the 4 in the equation.
So the y-intercept or the b is 4.