tolong bantuin, gimana caranya?

[tex] \left[\begin{array}{cc}a&b\\c&d\end{array}\right] \left[\begin{array}{ccc}1\\4\end{array}\right] = \left[\begin{array}{ccc}25\\8\end{array}\right] [/tex]
 
 a+4b = 25
c+4d = 8

-3a +b = 3
-3c + d =2

a+4b =25    (x1)  a+4b = 25
-3a + b = 3  (x4) -12a +4b = 12
                         13 a = 13
                           a = 1
1 + 4b = 25
4b = 24
b = 6

3c + 12 d = 24
-3c +d = 2
   13 d = 26
d = 2
c + 4(2) = 8
c = 0
a+b+c+d = 1 + 6 + 0 + 2 = 9  (jawab E)

gini :
a+4b = 25
c+4d = 8 

-3a +b = 3
-3c + d =2

a+4b =25    (x1)  a+4b = 25
-3a + b = 3  (x4) -12a +4b = 12
                         13 a = 13
                           a = 11 + 4b = 25
4b = 24
b = 6

3c + 12 d = 24
-3c +d = 2
13 d = 26
d = 2
c + 4(2) = 8
c = 0
a+b+c+d = 1 + 6 + 0 + 2 = 9 
jadi jawabannya yang benar (e)