A shop sells toilet rolls in small packs and big packs. There are 4 toilet rolls in a small pack. There are 9 toilet rolls in a big pack. The shop has s s\,s small packs and b b\,b big packs of toilet roll.
Show that an expression for the total number of packs of toilet roll the shop has is s+bs+bs+b.
Show that an expression for the total number of toilet rolls the shop has is 4s+9b4s+9b4s+9b.
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