The standard form of an equation of a line is y=mx+b. Our example equation will be 15=5x+3. The y-intercept would be when x=0, and the slope is m. We need to use algebra to find the y-int, but we can find the slope with just the equation. m=5.
To find the y-int, we need to set x as zero. This is because the intercept will be on an axis, therefore x is zero.
15=5(0)+3
15=0+3
15=3
y=3
The y-intercept is 3. The slope is 5.