Note that you must take 3460:209 Computer Science I, not 3460:101 Essentials of Computer Science.

Take

3450:335 Ordinary Differential Equations

and any three of the following:

3450:421 Advanced Calculus I

3450:422 Advanced Calculus II

3450:412 Abstract Algebra II

3450:415 Combinatorics and Graph Theory

Total: 9 additional credits, because you must already choose between Advanced Calculus I and Combinatorics.

Minor: No additional courses required.