She has 31 crayons because she bought 4 packs of crayon in which there are 8 crayons in each pack. But she opens ONE box and theres 7. So you'd do 4 times 8 and then minus 1 since one crayon is missing. Or you could do 3 times 8 since the 3 boxes has 8 crayons and then take the product of that and add 7. Hope this helps!
