HP Prime - Using the Solver App with custom, multi-character variables (Part 3)

How to use custom, multi-character variable names with the HP Prime solver app -- "Part 3" shows how you can use the results of the solver in other computations
Link for Part 1: • HP Prime - Using the S...
Link for Part 2: • HP Prime - Using the S...

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I'm having problems using variables from different Export
Eg:
EXPORT a,e,i,o,u;
EXPORT b,c,d.
I can make X=a*b, but I can't use X=a*e. Can you help me?