x = nr. de elevi
in orasul A au dormit cate 4 in camera : x/4
in orasul B au dormit cate 2 in camera : x/2
in orasul C au dormit cate unul in camera : x
[tex] \frac{x}{4}+ \frac{x}{2}+x=84 \\ \\ \frac{x}{4}+ \frac{ {2}) x}{2}+ ^{4)} x=84 \cdot 4 \\ \\ x+2x+4x=336 \\ \\ 7x=336 \\ \\ x = 48[/tex]
48 de elevi au fost in excursie