设平行四边形两边为a、b,两条对角线为4k、6k
2a + 2b = 68 a + b = 34
由题意：（a + 2k + 3k ) + （b + 2k + 3k ) = 80
( a + b ) + 10k = 80
34 + 10 k = 80
k = 4.6
4k = 18.4 6k = 27.6