A.)n + d = 20 and n + d = 1.40

That's wrong because if n + d = 20, it can't equal 1.40 too!  


B.)n + d = 20 and 5n + 10d = 1.40

That's wrong because the left side of 5n + 10d = 1.40 is in
cents but the right side is in dollars.


C.)n + d = 20 and 5n + 10d = 140

That's right, for the left side of 5n + 10d = 140 is in cents
and the right side is also in cents, because $1.40 equals 140 cents.

Edwin