If →a and →b are perpendicular vectors, |→a + →b| = 13 and |→a| = 5, find the value of |→b|.

Given: |→a + →b| = 13
|→a| = 5
|→a + →b|² = |→a|² + |→b|² + 2|→a|.|→b|cosθ
13² = 25 + |→b|² + 2|→a|.|→b|cos90°
169 = 25 + |→b|²
169 - 25 = |→b|²
|→b|² = 144
|→b| = 12