Answer: 
Step-by-step explanation:
You can do long division, which is very very hard to show with typing on a keyboard. You essentially want to divide the leading coefficient for each term. Ill try my best to explain it.
Do
. Write 2x^2 down. Now multiply (x - 3) by it. Then subtract it from the trinomial.

Now do
. Write that down next to your 2x^2. Multiply 3x by (x - 3) to get:

Your final step is to do
. Write this -2 next to your other two parts
Multiply -2 by (x - 3) to get:

Our remainder is 0 so that means (x - 3) goes into that trinomial exactly:
times
0.4x + 3.9 = 5.78
1. Subtraction property of equality:
Subtract 3.9 from both sides of the equal sign:
0.4x = 1.88
2. division property of equality:
Divide both sides of the equal sign by 0.4:
X = 4.7