Question 859504
You have a choice of trying the solution multistep or putting it altogether in a single proportion.

Area to volume, or volume to area, your choice.  


{{{1/300=v/(4*200)}}} and v is used as the number of gallons of this paint to use.
In case v is not a whole number, round UPward.


Note, I chose gallons to area, because now you simply multiply left member and right member by {{{4*200}}} to solve for v.  




You should find {{{v=8/3}}}, not a whole number.  Need 3 gallons ( because {{{2&2/3}}} is not a whole number ).