Please tell me the answer to this question. Give a step by step explanation as well.

15d^2 +7d-4

Step-by-step explanation:

(5d+4)(3d-1)

FOIL

first 5d*3d = 15d^2

outer 5d(-1) = -5d

inner 4*3d = 12d

last 4*-1 = -4

Add together

15d^2 -5d+12d -4

15d^2 +7d-4

With graphs on paper you can visually see intersecting lines(one solution), identical lines
(infinite solutions), or parallel lines(no solutions).
This method works best for lines that have integers for solutions. The task of determining rational or irrational solutions from graphs is difficult.

The substitution method usually must be used for equations with higher exponents. The deawback of this method is having to work with fractions.

The elimination method is often the method of choice.
This method however requires that you learn to recognize when the systems produce parallel lines or have equations that represent the same lines.