Amanda has gone on 7 hikes x 8 = <<7*8=56>>56 hikes.
Steven has gone on 56 hikes + 15 hikes = <<56+15=71>>71 hikes.
Camila needs to go on another 71 hikes - 7 hikes = <<71-7=64>>64 hikes.
Camila will achieve her goal in 64 hikes / 4 hikes/week = <<64/4=16>>16 weeks.
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