I highly recommend using the unit circle; the answer is 1/2.
13 cm+ 13 cm= 26 cm, 26 cm is the answer to Part B.
There are no real numbers that can do that job.
There's a pair of complex numbers that can do it.
They are
4.5 + i23.23
and
4.5 - i23.23 .
' i ' = the imaginary unit = √(-1)