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.