Question

Marcus is making cookies. The recipe says 2 1/4

Answer 1

6 3/4 is the amout of cups he'll use 

1 Batch: 2 1/4
2 Batches: 4 2/4
3 Batches: 6 3/4

Answer 2

we know that

The recipe says $2\frac{1}{4}$ cups of flour are needed for each batch

so

by proportion

Find how many cups of flour will Marcus use to make $3$ batches of cookies

Convert mixed number to an improper fraction

$2\frac{1}{4}=2.25$

$\frac{2.25}{1} \frac{cups}{batch} =\frac{x}{3} \frac{cups}{batch} \\ \\x=2.25*3\\ \\x=6.75\ cups$

Convert to a mixed number

$6.75\ cups=6+0.75=6+\frac{3}{4}=6\frac{3}{4}\ cups$

therefore

the answer is

$6\frac{3}{4}\ cups$