The atomic mass given on the periodic table is the mass of one mole of the element (relative to the mass of 1/12 of carbon 12.) There are 6.022 x10^23 molecules of any atoms in a mole. Therefore when it asks for the mass of 6.02 x 10^23 atoms it's asking what is the mass of one mole of Calcium.
The answer, therefore, is 40.08 as it states the atomic mass of calcium is 40.08