Hey there! 
2x + 3x = 20 + x
5x = 20 + x
20 + x = 5x 
SUBTRACT x to BOTH SIDES
5x - x = 20x + x - x
5x - 1x = 20x + 1x - 1x 
SIMPLIFY IT! 
4x = 20
DIVIDE 4 to BOTH SIDES 
4x/4 = 20/4
SIMPLIFY IT! 
x = 20/4
x = 5
Therefore, your answer is: x = 5
Good luck on your assignment & enjoy your day! 
~Amphitrite1040:)