Suppose the amu had been defined as 110th of the mass of a phosphorus atom. what would be the relative mass of carbon-12?

The relative mass of carbon would be

Explanation:

The amu is defined as 1/12 of the mass of a atom, thus according to the definition, the relative mass of carbon is exactly 12. If the definition of the AMU changed, we could calculate what the new relative mass is by dividing the relative mass of  by the mass of the new AMU in old AMUs.

The atomic weight of Phosphorus is 30.973, therefore  an amu would be  in old AMUs, if the atomic weight of carbon is 12.00, then in the new amu:

c. 4.54 x 10–12 j happens to be correct