let the balloon pump be m and one pack of balloons be n.
we will use the given data to calculate the the price of balloon pump (m) as well as the price of one pack of balloons (n). Then, we will use these prices to calculate the requirement.
First, we know that 1 balloon pump (m) added to 3 packs of balloons (3n) costs 9£
this means that: m + 3n = 9
therefore: m = 9 - 3n .................> equation 1
Then, we know that one pump (m) and 4 packs (4n) cost 11£.
this means that: m + 4n = 11 ..........> equation 2
Substitute with equation 1 in 2:
9 - 3n + 4n = 11
n = 11 - 9
n = 2£
Substitute with the value of n in equation 1:
m = 9 - 3n = 9 - 3(2) = 9 - 6 = 3£
we know to know the price of one pump and eight packs:
price = m + 8n = 3 + 8(2) = 3 + 16 = 19£
