x分之6=7分之2
2x=6×7
2x=42
x=21
x:0.3=0.4:0.8
0.8x=0.3×0.4
0.8x=0.12
x=0.12÷0.8
x=0.15
1.5分之0.75=6分之x
1.5x=6×0.75
1.5x=4.5
x=3