Answer:
book 25; pen 8
Explanation:
If we let b and p represent the cost of a book and a pen, respectively, then the two purchases can be written as ...
7b +4p = 207
5b +5p = 165
Multiply the second equation by 4/5 and subtract the result from the first equation:
(7b +4p) -4/5(5b +5p) = (207) -4/5(165)
3b = 75 . . . . simplify
b = 25 . . . . . divide by 3
Dividing the second equation by 5 gives ...
b + p = 33
Solving for p, we have ...
p = 33 -b = 33 -25 = 8
The cost of an exercise book is 25; the cost of a pen is 8.