Since the answer is increasing, we want to essentially draw a straight line and guesstimate where the 7th day is. To do this, we can only use the range out of the options given so that we can find a difference in the numbers, not the average. Finding the average (or anything else other than range) would give us a straight line, not an increasing one.We use the first and last day since they're the lowest and highest numbers respectively, and therefore have 67-43=24 as our range. To make this into a line, we can realize that the slope is (change in y)/(change in x). Since the degrees is the y axis and the day is the x axis, 24/(6-1)=24/5=4.8 is our slope. SInce we have the point (1, 43), we can have the equation y=mx+b=y=4.8x+b and plug in 1 and 43 to get 43=4.8*1+b. Subtracting 4.8 from both sides, we get 43-4.8=38.2=b, making our equation y=4.8x+38.2 (since y and x stay variables). For the 7th day, we would have 7 as our x value, making the temperature equal to 4.8*7+38.2=71.8
