Lens meter questions!

Hi, I've been trying this question and just want to check if I'm doing anything wrong (or right) as the case may be!:eek:

1. A lens meter (lens clock), calibrated for a refractive index of 1.523, is used to
   measure the front and back surface powers of a toric spectacle lens. Whenapplied to the front surface of the lens the lens meter gives values of +5.00Dalong 90 degrees and +7.50D along 180 degrees. When applied to thespherical back surface the lens measure gives a value of -3.00D. The centrethickness of the lens is 1cm and the refractive index is 1.700. What is theback vertex power of the spectacle lens? Express your answer in negativesph-cyl form with the powers correct to two decimal places. (11 marks)
   

I get +6.20/-3.41x90?

Lens meter questions!