60*(с*3)=189720180*с=189720
с=189720:180с=1054
<span>60*(с*3)=189720</span>
<span>60*3с=189720</span>
<span>3с=189720:60</span>
<span>3с=3162</span>
<span>с=3162:3</span>
<span>с=1054</span>