Link to the video on Educreations:
http://www.educreations.com/lesson/view/p-d-z-d-0-5878/2130240/?ref=appemail
You should draw a sketch of the region before you go for a calculator - draw it out and try to express everything in terms of left cumulative areas - then you can figure out the z scores -
Follow this link to Educreations:
http://www.educreations.com/lesson/view/5-2-23/2157364/?ref=appemail