kak tolong dong pakai caranya ya

misal penghapus = x
          buku = y
3x=2y ⇒ y = 3x/2
2x + 3y = 10.400
2x + 3 ( 3x/2 ) = 10400
2x + 9x /2 = 10400
13x/2 =10400
13x = 20800
x = 1600

3x = 2y
3 (1600) = 2y
4800 = 2y
y = 2400

jadi, x + 4y = 1600 + 4(2400)
                  = 1600 + 9600
                  = 11200 (c)