since you're given with the rectangular coordinates as (12,5), first thing to do is get the value of 'r' using the idea of pythagorean theorem. so you'll have 'r' as:
r² = 12² + 5²
r² = 169
r = 13
getting the angle, you'll have:
x = r cos α
or cos α = x/r
y = r sin α
or sin α = y/r
let's have cosα
cos α = 12/13
α = arccos 12/13
α = 22.62degrees
then you'll have the polar coordinates as :
(r,α)
(13, 22.62degrees)
