Question 904341
a+b=12,
15*a+40*b=255
a=12-b
15*(12-b)+40*b=255
180-15b+40*b=255
25*b=75
b=3
a=12-b
a=9 at $15 and  b=3 at $40
check
9+3=12
15*a+40*b=255
15*9+40*3=255
135+120=255
255=255
ok