So, we can say that #t = 20c# and that #3p = 12c#
From there, we need to find out how long it takes to paint #7# chairs. So, well make a ratio. If it takes #1t# to paint #20c#, how many #t# does it take to paint #7c#?
#20/1 = 7/?#
#7 = 20 xx ?#
#? = 7/20#
So it takes #(7t)/20# to paint #7# chairs
Now we solve for #t#
#3p = (3t)/5#
#15p = 3t#
#t = 5p#
Now we need to find how many liters of paint Mr.Lee needs after #4# hours
Well first, let's rewrite #20c = t# in terms of #c#
#c = t/20#
Now let's substitute #t/20# for #c# in the other equation
#3p = 12 xx t/20#
#3p = (3t)/5#
#15p = 3t#
#t = 5p#
So now if we have #4t#:
#4t = 20p#
So, if Mr. Lee paints for #4# hours he'll need #20# liters of paint
So, in #t# amount of time, Mr. Lee needs 5 liters of paint. But how many chairs can he paint
