The net force on the mass in the vertical direction is
∑ F = n - w = 0
and the net horizontal force is
∑ F = A - f = ma
where
n = magnitude of the normal force
w = mg = weight of the mass
m = 10 kg, mass of the … uh, mass
g = 9.8 m/s², mag. of acceleration due to gravity
A = 69 N, mag. of the applied force
f = mag. of kinetic friction
From the first equation, we get
n = mg = (10 kg) (9.8 m/s²) = 98 N
Then the friction force has magnitude
f = µ n = 0.5 (98 N) = 49 N
Solve the mass's acceleration in the second equation:
69 N - 49 N = (10 kg) a
a = (20 N) / (10 kg) = 2.0 m/s²
in the positive x direction.