Question 51073
When solving equations remember order of operations: 
PEMDAS (perenthesis, exponents, multiplication, division, addition, subtraction)in that order!
3x - 2(25 - 3x)= 40
First lets eliminate the parenthesis by distribution. 
Multiply -2(25) and -2(-3x)
3x -50 + 6x = 40
now we can combine like terms.
9x -50 = 40
If we add 50 to both sides of the equation, we can isolate the 9x.
9x = 90
Now in order to solve for x we can divide both sides by 9.
x = 10
Thats it.
Good luck!