Both statements together are sufficient, but neither alone is sufficeint
v3 - k3 ... assuming, v and k are the tenth digit of the numbers...
1)
v-k=6 alone give many possibilities..
2-(-4)... 8 - 2 so, v3-k3 is not known....
so, this stmt alone is not sufficient
2)
vk>0 ... can lead to many choice where both v and k are of same sign (+ve or -ve)
so, this stmt alone is not sufficient
3) Taking both together
vk > 0 ... means, both v and k are of same sign and none of them is zero
v -k = 6 , gives following options
assuming, both v and k are postive
v = 7,8,9 and k = 1,2,3 respectively
in all these 3 case, v3-k3 = 60
assuming, both v and k are negetive
v=-1,-2,-3 and k = -7,-8,-9 respectively.
in all these 3 case, v3-k3 = 60
4) So, Both statements together are sufficient, but neither alone is sufficeint