Hello!
Let's applicate formula:
F - Ff = ma
How we dont know friction force, we descompose it in:
F - (μ * N) = ma
Now, lets replace (N = Is the normal force, or weight in this case):
18 N - (μ * (64 kg * 9,81 m/s²) = 64 kg * 1,5 m/s²
First, lets resolve parenthesis:
18 N - (μ * 627,84 N) = 96 N
The force happens to subtract:
- (μ * 627,84 N = 96 N - 18 N
-μ = 78 N / 627,84 N
-μ = 0,124
The value of μk = 0,124
