1 mile = 5280 feet
81 * 5280 = 427680 feet per hour
1 hour = 3600 seconds
427680 / 3600 = 118.8 feet per second
118.8 * 15 = 1782 feet in 15 seconds
Linear not sure ...........
This year = 18kg
18 x .3= 5.4
The percentage change would be 5.4%. If it needs to be rounded by the nearest tenth, then it would be 5%.
I’m pretty confident this is the answer but I’m not 100% sure. I hope this helps!