[tex]Fie~x~nr.~elevilor: \\
x=5\cdot c_{1}+4\Rightarrow x-4=5\cdot c_{1}+4 \\
x=6\cdot c_{2}+4\Rightarrow x-4=6\cdot c_{2}+4 \\
x=7\cdot c_{3}+4\Rightarrow x-4=7\cdot c_{3}+4\\
c.m.m.m.c=210~\rightarrow~\text{Multiplu~al~lui~210~intre~800~si~900:~~\underline{840}} \\
x-4=840\Rightarrow~\text{In~scoala~sunt~\boxed{844~elevi.}}[/tex]
