If you draw the little triangle showing weight, thrust and drag in the climb then you find that angle of climb is Thrust minus Drag divided by Weight x Cos Climb angle.

 

At small climb angles, the sort of angles we get with transport aircraft, the Cosine of the climb angle is very nearly one, so we can say that the climb angle is (T-D)/W

 

The question gives you two engines at 28,000N each, so T is 56,000N

 

Aeroplane mass is 50,000kg, so weight is 500,000N (Mass x g)

 

Assume for small climb angles that L = W. Lift/drag ratio is 12, so drag is 500,000/12 = 41,667N

 

Put these figures into the climb equation:

 

Angle of climb = (56,000 - 41,667)/500,000 = 0.02866

 

Now at small angles this is the climb angle in radians and therefore approximately both Sin and Tan of the climb angle. Tan of the climb angle is the actual gradient. To get a percentage gradient you multiply by 100, and the answer is 2.866, or 2.9.