$\displaystyle \sum \tau = 0$ about point B.
$\displaystyle 2.5\cos(45) \cdot 6 = A \cdot 2$
$\displaystyle A = 7.5\cos(45) = 5.3$ kN
$\displaystyle \sum F_x = 0
$
$\displaystyle A = 2.5\cos(45) + B_x$
$\displaystyle B_x = A - 2.5\cos(45) = 3.54$ kN
$\displaystyle \sum F_y = 0
$
$\displaystyle B_y = 2.5\sin(45) = 1.77$ kN
$\displaystyle B = \sqrt{B_x^2 + B_y^2} = 3.95$ kN