Private is last to solve 10 and possibly 11 across assuming 5 is reversed (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Last letter of ( last to ) “ solve ” + X(Roman numeral for “10”) plus ( and ) CLUE(an example of which/possibly is 11 across) containing ( assuming ) reversal of ( … reversed ) [ V(Roman numeral for “5” + IS ].