Iknow what it saying but i'll already try many time but still can't find the correct answer pls teach me

From the information that it's an isosceles triangle. That means there are 2 (equal) sides - PR and PQ so the angles are also equal.
if you see that PQ and line Q are pararell so when there is a line like QR pass through them
the angle at R and at Q are the same equal X. This time you know that R angle is X so Q angle is X too. because they are the side which has same length as I told you at first.
and in triangle, the total angle is 180° then
70+X+X = 180, 70+2X=180 SO 2X=110 ---> X= 55°

HOPE THIS CAN HELP :)