Hope this helps with your questions :)
Let, speed of 1st bicyclist is x.
So, speed of 2nd bicyclist is x-3 .
We know, relative speed when two objects moves towards each other :

Now, distance travelled in 3 hours is (98-2) miles .
So,

Therefore, speed of bikes are 17.5 mph and 14.5 mph.
Hence, this is the required solution.
$800 increased by 25% = 1.25 x 800 = $1,000
Given a table, with an input (x) and output (y) , you could actually use the slope formula to get the rate of change because slope is the same thing as rate of change. If you recall, the slope formula is (y2-y1)÷(x2-x1)
Just pick two points from the chart and plug them in and that is your rate of change