So you would start from subtracting -4 on both sides then it leave 9x=-9 then divide both sides by 9 which would leave you with “ x=-18”
Answer:
3 gallons per mile, slope of 3
Step-by-step explanation:
To find out how many gallons the train uses per mile, look at the point (50,150). If you know that the train used 150 gallons to travel 50 miles, do 150/50 to get an answer of 3 gallons per mile.
For the second part, you know that as x increases by 1 (miles traveled) y (gallons) increases by 3, so therefore the slope is 3. You can also check this value by plugging in the points (150,450) and (50,150) into the 
Answer:
(6,8)
Step-by-step explanation:
midpoint=(x1+x2)÷2,(y1+y2)÷2
a(4,15) b(8,1)
x=4+8=12÷2=6
y=15+1=16÷2=8
Answer=(6,8)