If you stack the two diagrams together, you will get the height of two tables.
Looking at the first diagram, the extra height from the bottle (above table) is cancelled out by the bottle in the second diagram since it eats into the table’s height. Similarly the extra height from the can in the second diagram (above the table) is cancelled out by the can in the first diagram since it eats into the table’s height.
Since the extra heights are cancelled out, this means the total height of both diagrams is actually the height of two tables. So the answer is (1.5 + 1.1) ÷ 2 = 1.3m.
Another way to look at the question:
Table – Can + Bottle = 1.5
Table – Bottle + Can = 1.1
2 Tables = 2.6 (the Bottles and Cans cancel each other out)
1 Table = 1.3m