Answer:
\(B=\left(2x+1\right)^2+\left(3x-1\right)^2+2.\left(2x+1\right).\left(3x-1\right)+5\)
\(=[\left(2x+1\right)^2+\left(3x-1\right)^2+2.\left(2x+1\right).\left(3x-1\right)]+5\)
\(=[\left(2x+1\right)+\left(3x-1\right)]^2+5\)
\(=\left(2x+1+3x-1\right)^2+5\)
\(=\left(5x\right)^2+5\)
\(=25x^2+5\)