502 - (217-x) = 421
502-217+x=421
x=421-502+217
x=136
817 - (x+157) = 385
817-x-157=385
817-157-385=x
x=275
502 - (217-x) = 421
502-217+x=421
x=421-502+217
x=136
817 - (x+157) = 385
817-x-157=385
817-157-385=x
x=275