21.87-(313/х+8.74)=12.93
313/х+8.74= 21.87 - 12.93
313/х+8.74=8?94
313/х= 8.94 - 8.74
313/x=0.2
x = 313 : 0.2
x = 1565
21,87-(313/x+8.74)=1293
21.87-313/x-8.74=1293
-313/x=1293-21.87+8.74
-313/x=127.987
x=-313/127.987
x=-2.45