Answer:
I've never had to deal with this before but I would say C
I like the substitution method. Which is when you make one equation equal only x or y and plug it into the other equation)
There is also the graphing method. If you graphed it, it might not be quite as accurate (at least on hand, on computer you would be pretty exact)
Then there is the elimination method. You multiply one of the equations by a coefficient so that you can eliminate x or y from the equation.
The question only supplied us with the mass of the new baby which is:

This mass is too bizzarre & unrealistic for
The answer to that is 20x^4