They buy 7 backpacks for $8 each and fill each backpack with paper and pens that cost $5
Cost of 1 backpack = $8
cost of 7 backpacks = 8 * 7 = $56
Cost to fill each backpack with paper and pens = $5
Cost to fill each 7 backpacks with paper and pens = 5 * 7=$35
Total cost = $56 + $35 = $91
the students councils savings change by $91