Thanks for the comments and thumb-love.
Pingson, I was kind of regretting saying that as soon as I hit it...too much sharing? Anyway, she's remarkable. :)
DeSense, that made me chuckle: I was working out exactly that arithmetic when I read Professor P's reply, and with the same mental image of a school maths exam!
I'm ashamed to admit I had to do that manually. Still working on the solution, somewhat 24+x = (42+x):2 +7 ...
PS: Got it: above [-24: x = (42+x):2 -17 = x/2 +4 [x2, -x : x = 8)
Edited by DeSense - 2/4/14 at 2:48am