Answer:
13 quarters.
Step-by-step explanation:
Let d represent number of dimes and q represent number of quarters.
We have been given that the number of quarters is 6 more than the number of dimes. We can represent this information in an equation as:

We know that value of one dime is $0.10, so value of d dimes would be
.
We know that value of one quarter is $0.25, so value of q quarters would be
.
We have been given that Sally gave her brother $3.95 in quarters and dimes. We can represent this information in an equation as:

Now, we have a system of linear equation and we will solve our system by substitution method.
From equation (1), we will get:

Upon substituting this value in equation (2), we will get:







Therefore, Sally gave her brother 13 quarters.