Assuming that points P, T and T' are on a circle and the circle is centered on (0,0), coordinate of P indicates that the radius of the circle is 1. The distance from P to the point T means the arclength from P to T is x. In the case of a unit circle, the arclength is equal to the radian angle. The arclength from P to the point T' is π + x radians. Then the arclength from T to T' is π radians. This is equivalent to a rotation about the origin, which consist in transform coordinate (x, y) into (-x, -y). In consequence, if the coordinates of T are (3/5,4/5) then the coordinates of T' are (-3/5,-4/5).
We are given that x is the arclength from P(1,0) to T(3/4,4/5). In the case of a unit circle, the arclength from P(1,0) to a point T on a unit circle is equal to the radian angle that we rotate from the positive x axis up to T(3/4,4/5). So x is some radian angle. We don't actually have to solve for x, but you can find it using arctan (.8/.75) = 0.8176 radians or about 46°
Then we are told to add π to this x. If you add a rotation of π to a point on a circle, you are rotating that point by 180°. A 180° rotation about the origin is the same as a reflection about the origin. Recall that the transformation for a 180° rotation is (x,y) -> (-x, -y).
Therefore it should be T ' (-3/5, -4/5).
I have attached a link of the unit circle on a grapher https://www.desmos.com/calculator/rk4ridvpzr