下列函数中,在其定义域内既是奇函数又是减函数的是( )
A:y=-x3,x∈R
B:y=sinx,x∈R
C:y=x,x∈R
D:y=12x,x∈R
Last week, my father, mother and I visited the Great Wall,
3x-7×1.2=10.2
x=____