Does kilometers means the same as miles

No it doesn't. 
1 km = 0.62137 miles

No ,miles are 1.6 kilometers

It makes a 74 degree angle.

The sides of the triangle that are given are the side adjacent to the angle the ladder makes with the ground and the hypotenuse of the triangle.  

adjacent/hypotenuse is the ratio for cosine:

cos x = 7/25

To solve this, we will take the inverse cosine:

x = cos⁻¹(7/25) = 73.7 = 74