Here's link to the answer:

A scientific theory is a validated explanation of some aspect of the natural world, based on multiple facts that have been frequently verified through research and experimentation. Fact theories are not "guesses" but reliable accounts of the real world.
analyze problem
no need for distance formula
same x, only need to subtract y
3a-0=3a
X+y=3
Subtract x from both sides
y=-x+3
Substitute
2x--x+3=6
2x+x+3=6
3x+3=6
Subtract 3 from both sides
3x=3
Divide both sides by 3
x=1
79, 000
Tip: focus on the number/place you need to round from ( in this case 8) if the number is 4 or below it will stay the same, but if the number is 5 or above it will change by 1 number (in this case it will change from 78, 045 to 79, 000)