Answer
$296.482\ amu$
Work Step by Step
To get the relative atomic mass of the element, we need to multiply the relative masses of the isotopes with their abundance and add them together. As in this case we have the masses of isotopes measured relative atomic mass of ${^{12}C}$, we can obtain the relative atomic mass of Wt element by multiplying its masses relative to ${^{12}C}$ with their natural abundances. Then we add together the obtained values and multiply them with the amu mass of ${^{12}C}$. The mass of carbon is 12 amu.
$Mr_{Wt}= (24.6630\times0.72+24.7490\times0.04+24.8312\times0.24)\times 12\ amu= 296.482\ amu$
