First, let's convert every single measurement into feet from meters so we don't have to worry about it later.
We have 12m0.3048m/ft=39.3701ft for the height
And we have 120m0.3048m/ft=393.7007ft for the length.
Now, we can find the total area of the wall. We do length times height, so we have
(39.3701ft)(393.7007ft)=15,500.0359ft2
Now, we do some ugly math. We must divide by the gallons.
Since each gallon of paint covers 150, we must do
15,500.0359sqft150sqft/gallon=103.3335gallons
Since you can't actually by a fraction of a gallon, we must round up.
So, we simply have
104 gallons as our answer.
So 104 is our answer.
Thanks! :)