Determine the value of x, y and z, in alphabetical order for each diagram. (Give a reason for your answer)

The angles on a straight line add up to $180^\circ$.

$$\angle PQT + \angle TQS + \angle SQR = 180^\circ$$

Substitute the given angle measures:

$$70^\circ + 80^\circ + (y+10^\circ) = 180^\circ$$

Combine the constant terms:

$$160^\circ + y = 180^\circ$$

Subtract $160^\circ$ from both sides:

$$y = 180^\circ - 160^\circ$$ $$y = 20^\circ$$

Reason: Angles on a straight line.
The value of y is $\boxed{20^\circ}$.

When two straight lines intersect, the angles opposite each other are called vertically opposite angles, and they are equal.

$$x = 50^\circ$$

Reason: Vertically opposite angles are equal.
The value of x is $\boxed{50^\circ}$.