Recycling 1 tonne of paper will save 24 trees. If 4 schools each recycle $\frac{3}{4}$ of a tonne of paper, then the total number of trees this will save is
(A) 24
(B) 72
(C) 18
(D) 126
(E) 80
If 4 schools each recycle $\frac{3}{4}$ of a tonne of paper, then combined, they recycle $4 \times \frac{3}{4}=\frac{12}{4}=3$ tonnes of paper.

Since recycling 1 tonne of paper will save 24 trees, recycling 3 tonnes of paper will save $3 \times 24=72$ trees.

ANSwER: (B)

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