Question 796435
Hi there, simple algebra skills are required remember change the side = change the sign..

{{{5x+1=21}}}

5x = 21 - 1 (notice + becomes - and vice versa)
5x = 20 (simplified 21-1)
x = 20/5 (notice * becomes / and vice versa)
x = 4 (simplified 20/5)

There is your proof that 5x +1 = 21 gives x = 4