Erica bought 3 1/2 yards of frederick if she uses 2/3 of the fabric to make a curtain how much will she have left

First, we need to convert 3 1/2 into an improper so we can multiply the two fractions.

3 1/2 
3*2=6
6+1=7
3 1/2 as an improper fraction would be 7/2

Now we multiply the fractions.
7/2*2/3
7*2=14
2*3=6
14/6
Now we can convert the improper fraction back into a proper fraction.

How many times does 6 fit into 14? 2 with a remainder of 2
The Fraction would be: 2 2/6 or reduced to 2 1/3
She used 2 1/3 yards of fabric.

The question asks for how much she has left so, we must subtract 2 1/3 from 3 1/2
However, we must have a common denominator to subtract.

To find this, we can list the multiples of both of the denominators:
2: 2,4,6,8,10
3: 3,6,9,12,15

The LCM (Lowest Common Denominator) is 6.
2*3=6
3*2=6

We must do the same for the numerator as what is done for one-half has to be done for the other.

1*3=3
1*2=2

The New fractions would be:
3 3/6
and 
2 2/6

Now we can subtract ;
3-2=1

3-2=1

We don't subtract the denominator

The answer is 1 1/6.

Erica would have 1 1/6 of the curtain left.

Hope this Helps! 
-Benjamin :)