答：由题意可得方程组：
{ x - 3y = 4 ①
x - 4y = 3 ②
由① - ②得 (x - 3y) - (x-4y) = 1 即 y = 1 ③
将③代入①可得 x - 3 = 4 则 x = 4 + 3 = 7
所以方程组的解为{ x=7
y=1.