The complete question is shown below. As you can see, we know that:
Shapes are congruent if you can turn one into the other by moving, rotating or flipping. If any two triangles have matching side lengths, they're not necessarily congruent. The same happens if they have two matching side lengths, but If triangles have three matching side lengths, then they must be congruent. This is is known as the Side-Side-Side Postulate (SSS). Since in this problem corresponding sides measures the same, therefore we can say that the postulate that applies is:
We know that for example 2/4=4/8 so it is multiplied by 2. In this problem the fractions are 2 2/4 and 6 1/8. We are subtracting so you would first multiply the fraction that’s going to subtracted from the other fraction 2 3/4= 2 6/8. Now that we have our fractions we can subtract 6 1/8-2 6/8 this would leave us with 3.375 which is equal to 3 3/8.