x+12等于4 xxx等于8.4 x+3.2得4.6 x-1.8的4 x-2得15 1.6x的6.4 x/7得0.3 x/3的2.1 怎么解

x+12=4
x=4-12
x=负8
xxx=8.4
2.1乘以2乘以2
=4.2乘以2
=8.4
x+3.2=4.6
x=4.6-3.2
x=1.4
x-1.8=4
x=4+1.8
x=5.8
x-2=15
x=15+2
x=17
1.6x=6.4
x=6.4除以1.6
x=4
x除以7=0.3
x=0.3乘以7
x=2.1
x除以3=2.1
x=2.1乘以3
x=6.3