Penyelesaian dari persamaan 3c-5y=11 dan 4x+y=7 adalah a dan b, maka a+b adalah

3x - 5y = 11

4x + y = 7
y = 7 - 4x

3x - 5y = 11
3x - 5(7 - 4x) = 11
3x - 35 + 20x = 11
23x = 11 + 35
23x = 46
x = 2

y = 7 - 4x
y = 7 - 4(2)
y = 7 - 8
y = -1

x = a = 2
y = b = -1

a + b
2 + (-1)
1

3c = 3x? kan
3x-5y=11
4x+y=7
x=a
y=b

a+b..?

3a - 5b = 11 Ι*1
4a + b = 7 Ι*5
___________
3a - 5b = 11
20a + 5b = 35
___________ - 
-17a = -24
a = -24/-17
a = 24/17

3a - 5b = 11
3(24/17) - 5b = 11
72/17 - 5b = 11
72/17 - 11 = 5b Ι*17
________________
72 - 187 = 85b
-115 = 85b
-115/85 = b

a + b
= 24/17 + (-115/85)
= 24/17 - 115/85
= 1800/1275 - 1725/1275
= 75/1275 Ι :75
___________
= 1/17.

Thx.