How do i find the atomic m of carbon.Two isotopes:carbon-12 m of 12.00amu and carbon-13 m of 13.00amu?

I just need to know how to find the atomic m of carbon. It has two isotopes carbon-12 with a m of 12.00amu and carbon-13 with a m of 13.00amu their relative abundances are 98.9% and 1.10%