gcse chemistry question - 6 marks

Some students investigated the thermal decomposition of metal carbonates.
The word equation for the reaction is:
metal carbonate → metal oxide + carbon dioxide
The students made the following hypothesis:
‘When heated the same mass of any metal carbonate produces
the same mass of carbon dioxide.’
The students heated a test tube containing copper carbonate.
Table 1 shows their results:

Time the test tube containing copper
carbonate was heated in mins | 0 | 2 | 4 | 6
Mass of test tube and contents in g | 17.7 | 17.1 | 17.0 | 17.0

Plan a method the students could use to test their hypothesis.
You should show how the students use their results to test the hypothesis.
You do not need to write about safety precautions.