Please help and show work if you can I only need 10, 11 and 12

Step-by-step explanation:

10). AD = BC [If ABCD is a parallelogram]

     3x + 1 = 6x - 4

     6x - 3x = 1 + 4

     3x = 5

     x =

11). If ABCD is a parallelogram,

     AB = CD

     5x - 8 = 2x + 7

     5x - 2x = 7 + 8

     3x = 15

     x = 5

12). If ABCD is a parallelogram,

     AB = CD

     AB║CD and BD is a transversal intersecting these parallel lines.

     ∠ABD ≅ ∠BDC [Alternate interior angles]

     4x - 1 = x + 38

     4x - x = 38 + 1

     3x = 39

     x = 13

(n^3 - n)

= n(n-1)(n+1)

since it is divisible by 3 and 2 ,because it is a multiple 3 consecutive number

if, n-1 is odd then n+1 is also odd, then it is a multiple of 9

but if, n-1 is even then n+1 is also even, then it is a multiple of 4

so, largest multiple = max(9*2, 4*3) = max(18, 12) = 18