Se 15a-b/3=4 e 3a-b/6+3a-b/4=quatro terços então o valor de a+...

(15a-b)/3 = 4 --> 15a - b = 12 --> 15a = 12+b --> a = (12+b)/15
(3a-b)/6+ (3a-b)/4 = 2(a+b)/3
mmc (6,4,3) = 12
2(3a-b) + 3(3a-b) = 8(a+b)
6a-2b+9a-3b = 8a+8b
15a-5b = 8a+8b
15a-8a = 8b+5b
7a = 13b
a = 13b/7
(12+b)/15 = 13b/7
7(12+b) = 195b
84+7b = 195b
195b-7b = 84
188b = 84
b = 84/188
b = 21/47
a = 13b/7
a = (13.21 / 47) . 1/7
a = 13.3/47
a = 39/47
a+b = 39/47+21/47
a+b = 60/47​