If a=(25x + 1)°, c=(25x -2)° and d=(20x - 1)°, find d.

We are asked to find the angle D given that we have the three angles of a triangle and we also know that the summation of all angles in a  triangle is equal to 180°. Thus, the solution to this problem is shown below:
∠A = (25X + 1)°
∠C = (25X - 2)°
∠D = (20X -1)°
180° = (25X + 1)° + (25X -2)° + (20X -1)°
180° = 25X + 1+25X -2 +20X -1
180° = 70X  - 2
180° + 2 = 70X
182/70 = 70X / 70
2.6 = X

Since we already know that the value for x is equal to 2.6, we can now solve for D such as the solution is shown below:
∠D = 20x -1
∠D = (20*2.6) -1
∠D = 51°

The answer for the value of D is equal to 51°.