As AC is the diameter of the circle, the measument of angle B will be 90 degrees.
The measurement of angle C can be determined as,
![\begin{gathered} \angle A+\angle B+\angle C=180^(\circ) \\ 40^(\circ)+90^(\circ)+\angle C=180^(\circ) \\ \angle C=50^(\circ) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/3xv9hyugoaxl0r0w00qr10jthcut8k293s.png)
Thus, measure of angle C is 50 degrees.
The measure of arc BC can be determined as,
![\begin{gathered} \text{mBC}=2*40^(\circ) \\ =80^(\circ) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/2i6ere7mhpxxumeyz4vjacgrn5vcmk0k5g.png)
Thus, arc BC subtends 80 degrees at the center.