<u>ANSWER</u>
It is not one-to-one function
<u>EXPLANATION</u>
A one-to-one function must pass the horizontal line test.
The graph described in the question looks like the one in the attachment.
A horizontal line drawn in red cuts the graph at more than one point.
Therefore the parabola shown facing up with a vertex 
is not a one-to-one function.
2x+5=x-8
-x on both sides
x+5=8
-5 on both sides
x=-13
4 kilometres is 4000 meters
4000 meters - 3400 meters = 600 meters
and as John is the one that rode 4 kilometres he rode further and by 600 meters
(67 + 68 + 78 + x) / 4 = 70
(213 + x) / 4 = 70
213 + x = 70 * 4
213 + x = 280
x = 280 - 213
x = 67
(213 + x) / 4 = 79
213 + x = 79 * 4
213 + x = 316
x = 316 - 213
x = 103
lowest u can make is 67, highest u can make is 100
