Slope-intercept form is:
y = mx + b
"m" is the slope, "b" is the y-intercept (the y value when x = 0)
(there is probably another way to do this, but I will be doing it this way)
Isolate the "y" in the equation
3x + 4y = 12 Subtract 3x on both sides
4y = 12 - 3x Divide 4 on both sides
or 
The slope is -3/4
For lines to be parallel, they have to have the SAME slope. The given line's slope is -3/4, so the slope of the parallel line is also 
Answer:
The numerical length of BD is 20 units
Step-by-step explanation:
Let us solve the question
∵ Point C lies on the line segment BD
→ That means C divides BD into 2 parts
∴ C divides BD into 2 parts BC and CD
∴ BD = BC + CD
∵ BD = 5x
∵ BC = 4x
∵ CD = 4
→ Substitute them in the equation above
∴ 5x = 4x + 4
→ Subtract 4x from both sides
∵ 5x - 4x = 4x - 4x + 4
∴ x = 4
→ Substitute the value of x in the expression of BD
∵ BD = 5x
∵ x = 4
∴ BD = 5(4) = 20
∴ The numerical length of BD is 20 units
