For small angles of climb, climb angle is T-D/W. Three engines give
90,000N thrust. Aircraft Mass is 50,000kg, so weight is 500,000N. Drag is 1/10
of lift, equals 50,000N
Climb angle (or gradient, it’s the same thing at small angles) is:
(90,000 - 50,000)/500,000 = 0.08radians
This is about 4.5deg, or 8.0% (from the answer 4 up in 50 along)