The value of sin B - cos A is;

1. $\dfrac{1}{2}$

2. 1

3. 0

4. none of these

Since ΔABC is a right angled triangle.

By formula,

sin θ = $\dfrac{\text{Perpendicular}}{\text{Hypotenuse}}$ and cos θ = $\dfrac{\text{Base}}{\text{Hypotenuse}}$.

So, sin B = $\dfrac{\text{AC}}{\text{AB}} = \dfrac{3}{5}$

cos A = $\dfrac{\text{AC}}{\text{AB}} = \dfrac{3}{5}$

The value of sin B - cos A = $\dfrac{3}{5} - \dfrac{3}{5}$ = 0.

Hence, option 3 is the correct option.