Question 1208899
Might be easier to first give variable a for Andrew's account.


Andrew, a
Beatrice, 3a-600


If the described condition, then {{{a+300=(1/2)(3a-600)}}}.

{{{2a+600=2a-600}}} (this step looks like a mistake)

{{{1200=5a}}}

{{{a=240}}}

Beatrice had {{{cross(3*240-600=720-600)}}}
or she had {{{cross(120)}}} dollars.