Calculate the mass units of .25 mol of carbon -12 atoms.

The molar mass of the Carbon-12 from the periodic table is given to be 12.011 g. Multiply this mass with the number of moles given.
                         (0.25 moles) x (12.011 g / mole) = 3 g
Thus, the mass of 0.25 moles of carbon-12 is 3 g. 

m=9

step-by-step explanation:

7m+8=71 subtract   8 from 71 which is 63 than divide it by 7m   equal 9.