15.
2(a+b) = 1
(a-b)/2 = 0.8(3)
--------------------
2a + 2b = 1 => a = (1 -2b)/2
a - b = 1.6(6) => 1 - 2b - 2b = 3.3(3) => 1 - 3.3(3) = 4b => b = -0.583(3)
a = 0.083(3)
16.
a + b =180
a/2 = b/3 + 65 | *2
a=2b/3 +130
2b/3 + 130 + b = 180
2b/3 + b = 50
5b/3=50
5b=150
b=30
=> a=150
150...................100
30.................... x
x = 30*100/150
=> x=20%
