The total weight of a toy rifle and a rubber ball is 3.5 kg. The total weight of a toy rifle and a toy plane is 5.9 kg. If the total weight of a toy plane and a rubber ball is 4.94 kg, find the total weight of the toy rifle, the rubber ball and the toy plane.
Let 1 toy rifle be 1 T.
Let 1 rubber ball be 1 R.
Let 1 toy plane be 1 P.

1 T + 1 R = 3.5 --- (1)
1 T + 1 P = 5.9 --- (2)
1 P + 1 R = 4.94 --- (3)

(1) + (2) + (3)
1 T + 1 R + 1 T + 1 P + 1 P + 1 R = 3.5 + 5.9 + 4.94
2 T + 2 R + 2 P = 14.34
2(1 T + 1 R + 1 P) = 14.34 

1 T + 1 R + 1 P = 14.34 ÷ 2
1 T + 1 R + 1 P = 7.17

 Total weight of the toy rifle, the rubber ball and the toy plane = 7.17 kg

Answer(s): 7.17 kg