This question assumes that lift = weight and thus the following formula can be used:

 

Gradient = (thrust/weight - drag/lift) x 100%

 

Mass of aircraft = 50,000kg = 50,000 x 10 = 500,000N

 

Total Thrust = thrust per engine x No. of operating engines.

 

In this question it states that although it is a twin engine jet aeroplane one engine is inoperative.

 

Total thrust = 60,000 x 1 = 60,000N

 

Inserting the information into the formula gives:

 

Gradient = (60,000/500,000 - 1/12) x 100

 

= (0.12 - 0.083) x 100

 

= 3.7%