Question

How do you know that all four sides of this shape are congruent?

Answer 1

Quadrilateral QRST is given as a parallelogram. Hence, opposite sides are congruent.

That is

Line segment QT is congruent to line segment RS

and

Line segment QR is congruent to line segment TS

Since it is given that QR is congruent to QT, then all the four sides of the quadrilateral QRST are congruent.