y=mx+b
m=slope
b=yint
two points
cost=y
(4,5.5) and (7,7.75)
slope=(y2-y1)/(x2-x1)
slope=(7.75-5.5)/(7-4)=2.25/3=0.75
y=0.75x+b
find b
(4,5.5)
x=4
y=5.5
5.5=0.75(4)+b
5.5=3+b
minus 3 fromboth sides
2.5=b
y=0.75x+2.5
3 hours
y=0.75(3)+2.5
y=2.25+2.5
y=4.75
answer is D