Gemetry

sin (x + 21)  = cos (2x + 21)

Since these are cofunctions....the angles add to 90°

So  we have

x + 21  + 2x + 21  = 90     simplify

3x + 42  =  90      subtract 42 from both sides

3x  =  48    divide both sides by 3

x = 16

Second one

The triangle on the left is a 45-45-90 right triangle....the hypotenuse = 2√2

And the other two sides are 1/√2  times the hypotenuse

So the   common side of both triangles  =  2√2 ( 1/√2) =  2

Since  the triangle on the right is a 30-60-90 right triangle, the side opposite the 60° angle, y, is √3  that of the side opposite the 30° angle......and the side opposite the 30° angle  = 2

So...y  = √3 * 2   =     2√3