I am a bit stuck on how to find the standard deviation of this question. I know the formula u need to use: x-(x bar) / Z .. But I dont know how to find the Z score!

Could you please help me with (1) find the Z score value and (2) getting to the answer...

The question being:

Monica walks to work from home and she uses route a or route b.

Her journey time, Y minutes by route B may be assumed to be normally distributed with a mean of 40 and an unknown standard deviation.

Given that P(Y > 45) = 0.12, calculate the standard deviation value.

I would really appreciate some helpful feedback and solutions!

Thanks in advance

Dan