4 11/15 - 1 7/12 = 71/15 -19/12 = (71*4-19*5)/60= (284 -95)/60 = 189/60= 3,15
-(315/100) / (84/10) = - 315/84
6/10*5/6 = 30/60 = 1/2
-315/84 + 1/2 = - 315/84 + 42/84 = -273/ 84 = - 3 1/4
3/7+4/9+4/7+5/9=(3/7+4/7)+(4/9+5/9)=7/7+9/9=1+1=2
1/11+1/5+4/11+4/5+6/11=(1/11+4/11+6/11)+(1/5+4/5)=11/11+5/5=1+1=2
1/15+4/15+1/18+5/18+2/21+5/21+1/24+7/24=(1/15+4/15)+(1/18+5/18)+(2/21+5/21)+(1/24+7/24)=5/15+6/18+7/21+8/24=1/3+1/3+1/3+1/3=4/3=1 1/3
<span>1/8+1/12+1/16+1/20+3/8+5/12+7/16+9/20=(1/8+3/8)+(1/12+5/12)+(1/16+7/16)+(1/20+9/20)=4/8+6/12+8/16+10/20=1/2+1/2+1/2+1/2=4/2=2</span>
...................................х= - 26\3
<span>скорость 6 км/ч = 6 *1000/3600 м/с = 1,67 м/с</span>