[Edit]
since each internal node can point to 10 nodes,
at each level, we have $10^h$ nodes, where h is height of tree. now since all keys are accommodated at the leaf nodes, and each leaf node can hold 9 keys,
$10^h \times 9 \geq 5000$
$ h \geq 2.7$
hence height of B+tree would be 3, and number of levels would be 0,1,2,3 = 4
Answer is 4
PS: thanks for pointing out the mistkae