It is asking you to convert them to different units of measurements.
Y = 9/2x is in slope intercept form (y = mx+b) where m represents the slope and b represents the y-intercept.
In this case, 9/2 is the slope.
Change 212,514 into 215,000.
Change 396,705 into 400,000.
--------
Estimate:
215,000 + 400,000 = 615,000
Therefore:
212,514 + 396,705 ≈ 615,000
2016 - 1921 = 95
Hope this helped!
Average speed = 
Ishan's Speed uphill = 10mph
Time taken = 18 minutes = 18/60 = 3/10 hours
Now distance = rate × time
Distance traveled by Ishaan up hill = 10 × 3/10 = 3 miles
Now returning back home
Distance = 3 miles
Rate = 30 mph
So time taken = distance/ rate = 3/30= 1/10 hours = 1/10 ×60 = 6 minutes.
Now total distance traveled = 3 + 3 = 6 miles
Total time taken = 18 + 6 = 24 minutes = 24/60 = 2/5 hours
Average speed
= 
= 15 mph
Ishaan's average speed for the entire trip from home to the gift store and back is 15mph