Question

s+f+t=564
s+f=345
f+t=364
________
s=? f=? t=?

Answer 1

s+f+t=564
s+f=345
f+t=364
________
s=? f=? t=?

t=564-345
t=219

s=564-364
s=200

f=345-200
f=145

Answer 2

s+f+t=564
s+f=345
f+t=364
(s+f+t) -(f+t) =564-364=200 (s)
200+f =345
f=345-200
f=145
145+t=364
t=364-145
t= 219