In congruent triangles, ASA (Angle-Side-Angle) is a condition where two triangles have one pair of corresponding angles equal and the included sides equal. In this case, since ΔPQR is congruent to ΔSTU under ASA, it means that angle P is equal to angle S, angle Q is equal to angle T, and the included side PR is equal to the included side ST. Therefore, the value of Y, which is the measure of angle Q, is equal to 90 degrees.