Question 1134087
Let x be the # of the $3.75 shares and y be the # of the $6.50 shares. So 

{{{system(x+y=600,3.75x+6.5y=3212.5)}}} 

{{{system(3.75x+3.75y=2250,3.75x+6.5y=3212.5)}}}

{{{-2.75y=-962.5}}}

{{{highlight(highlight_green(y=350))}}} 250 are $3.75 shares and 350 are $6.50.