Rule 700.2h

Some modal spells use plus signs (+) rather than bullet points, with each plus sign followed by a cost. This indicates that each mode has an additional cost that must be paid as the spell is cast if that mode is chosen. If more than one such mode is chosen, all additional costs must be paid to cast that spell. Paying these costs follows the rules for paying additional costs in rules 601.2b and 601.2f–h.

Find this number in the current Rules