Which ordered pair comes closest to the solution of the system of equations that includes the above equation and the equation y=0.25x + 3.9?

It would be A, (2,4). 

First off, you have two equations: y=1.8x+1.1 and y=0.25x+3.9. Since we can say y=y by using reflexive property, that would mean

1.8x + 1.1= 0.25x+3.9 .      If we simply from there..
-0.25x        -0.25x

1.55x + 1.1= 3.9 
          - 1.1      -1.1 

1.55x=2.8 and then dividing both sides by 1.55, you would get x= around 1.8. Since the problem says "Which number pair is the closest, we can round 1.8 to 2. Next, substitute in 2 into the equation y=0.25x+3.9 to make it
y= 0.25(2)+3.9, making y=4.35, but we can round that to 4. 

There you have it. x=2 and y=4, making it (x,y) into (2,4)