A 70-N block and an 35-N block are connected by a string as shown. If the pulley is mless and the surface i?

A 70-N block and an 35-N block are connected by a string as shown. If the pulley is mless and the surface is frictionless, the magnitude of the acceleration of the 35-N block is: here is the picture http://edugen.wiley.com/edugen/courses/crs4957/art/qb/qu/c05/q52_1.png , please show work , i dont understand how to get this