Question

tim x biet 

420:[75-(x*10)]=21

Answer 1

420:[75-(x*10)]=21

=> 75 - ( x*10) = 420 : 21 = 20

=> x *10 = 75 - 20 = 55 

=> x = 55 : 10 = 5,5

Answer 2

\(420:\left[75-\left(x\cdot10\right)\right]=21\)

\(75-\left(x\cdot10\right)=420:21\)

\(75-\left(x\cdot10\right)=20\)

\(x\cdot10=75-20\)

\(x\cdot10=55\)

\(x=55:10\)

\(x=5,5\)