Hilda has $210 worth of $10 and $12 stock shares. the number of $10 shares is five more than twice the number of $12 shares. how many of each type of share does she have?

Let n and v represent the numbers of $10 and $12 shares Hilda owns.
.. n = 2v +5 . . . . . the number of $10 shares is 5 more than twice the number of $12 shares
.. 10n +12v = 210 . . . Hilda has $210 worth of $10 and $12 shares

Using the expression of the first equation to substitute into the second, we have
.. 10(2v +5) +12v = 210
.. 32v +50 = 210 . . . . . . collect terms
.. 32v = 160 . . . . . . . . . . subtract 50
.. v = 5 . . . . . . . . . . . . . . divide by 32
.. n = 2*5 +5 = 15

Hilda has 15 $10 shares and 5 $12 shares.

C. 40,320 just did the math right now

The correct answer would be "convenience"