Firstly we start with the rule of 
BODMAS 
We solve the bracketss
6(2x-10)÷2=40
6(2x-10) 
12x-60 
then we do division 
12x-60÷2=40 
-60÷2
-30 
we write the equation as
12x-30=40 
since we are looking for the value of x 
we make x the subject..
12x-30=40
12x=40+30
12x=70
x= 5 10/12