tan25(100+x)=tan29(x)

Do you mean   tan(25(100+x)) = tan(29x)

if so. then

25(x+100) = 29x

25x+ 2500 = 29x

2500 = 4x

x = 625  (~ 265 + 360n)

or did you mean  tan (25) *(x+100) = tan (29) * x

                            tan 25/tan29 = x/(x+100)

                               x = 529.88