u = 27+2x --> du = 2 dx
change the value of upper/lower limits
and it will be easy O_o
I'm still not sure where you get this 277 from but the point of the last question was to check that you followed why I simply substituted 125 and 27 in for u instead of replacing it with the 27+2x, because i'm lazy and don't feel like substituting back in if I already know what it's going to be.
But here is the solution with substituting the 27+2x back in:
u goes from 27 to 125
x goes from 0 to 49
does that help?