We set up a system of equations to solve.
Let x = number books priced at $6.99 and y = number books priced $9.99.
There are 32 books bought so we have the equation:-
x + y = 32.................(1)
Now we get an equation from the costs of the books
6.99x + 9.99y = 256.68...................(2)
Solving this system of 2 equations:-
From equation (1):- y = 32 - x
Now substitute this into equation (2):-
6.99x + 9.99(32 - x) = 256.68
6.99x + 319.68 - 9.99x = 256.68
-3x = - 63
x = 21
From equation (1) y = 32 - 21 = 11
So Amber bought 21 books at 6.99 and 11 books at 9.99 dollars Answer