well, Mark has
1 1/3 of yellow paint
1 1/4 of green paint and
7/8 of blue paint
now, bear in mind, the yellow is a bucket and 1/3 more, the green one is one bucket and 1/4 more and the blue is 7/8 which is almost 8/8, so is almost a bucketfull.
Then he's going to use 3/4 of each, so, we'd have to subtract 3/4 from each, and there'll be some left still in the paint bucket.
How many will he have left altogether? well, we simply add the leftovers.
[tex]\bf 1\frac{1}{3}\implies \cfrac{1\cdot 3+1}{3}\implies \cfrac{4}{3}
\\\\\\
\cfrac{4}{3}-\stackrel{\downarrow }{\cfrac{3}{4}}\implies \cfrac{16-9}{12}\implies \boxed{\cfrac{7}{12}}\\\\
-------------------------------\\\\
1\frac{1}{4}\implies \cfrac{1\cdot 4+1}{4}\implies \cfrac{5}{4}
\\\\\\
\cfrac{5}{4}-\stackrel{\downarrow }{\cfrac{3}{4}}\implies \cfrac{5-3}{4}\implies \cfrac{2}{4}\implies \boxed{\cfrac{1}{2}}\\\\
-------------------------------\\\\[/tex]
[tex]\bf \cfrac{7}{8}-\stackrel{\downarrow }{\cfrac{3}{4}}\implies \cfrac{7-6
}{8}\implies \boxed{\cfrac{1}{8}}\\\\
-------------------------------\\\\
\textit{so the leftovers are }\cfrac{7}{12}+\cfrac{1}{2}+\cfrac{1}{8}\implies \cfrac{14+12+3}{24}\implies \cfrac{29}{24}\implies 1\frac{5}{24}[/tex]