In the clinic, you are handed the following power crosses written by your consultant.
 
 

a. Convert them into spectacle forms with minus cylinder notation 
(assumming that your consultant performed the retinoscopy at a working 
distance of 67 cm from the patient).

b. Convert them into spectacle forms with positive cylinder notation 
(assumming that your consultant had an elbow injury and can only achieved 
a working distance of 50cm from the patient).