7s + 9t - 63 = 0
s = ( 63 - 9t ) : 7 = 9 - 1 ( 2/7 )t
t = ( 63 - 7s ) : 9 = 7 - ( 7/9 )s
•••••••••••••
11u + 2v + 22 = 0
u = ( - 2v - 22 ) : 11 = - ( 2/11 )v - 2
v = ( - 11u - 22 ) : 2 = - 5,5u - 11
•••••••••••
25r - 4w - 100 = 0
r = ( 4w + 100 ) : 25 = 0,16w + 4
w = ( 25r - 100 ) : 4 = 6,25r - 25t