x * 4 + x * 7 + x * 9 = 40300
x * ( 4 + 7 + 9 ) = 40300
x * 20 = 40300
x = 40300 : 20
x = 2015
x*4+x*7+x*9=40300
suy ra x*(4+7+9)=40300
suy ra x*20=40300
suy ra x=40300:20
suy ra x=2015
vậy x=2015
X x 4 + X x 7 + X x 9 = 40 300
X x ( 4 + 7 + 9 ) = 40 300
X x 20 = 40 300
X = 40 300 : 20
X = 2015
\(x\times4+x\times7+x\times9=40300\)
\(x\times\left(4+7+9\right)=40300\)
\(x\times20=40300\)
\(x=40300:20\)
\(x=2015\)