from x15 to x 25 is 4 - -16 = -20 degree change
25 -15 = 10000 feet
-20/10 = -2 degrees every 1000 feet
The answer would be 11x-12
The anwer is 67/72 and can not be simpled any more
Only if the individual doing the calculation makes a substantial mistake.
Any fraction with the same quantity in the numerator and denominator
always has the value of ' 1 ', (provided only that the quantity is not zero).