Coupon Feature in Event Booking to be valid only

Coupon Feature to to allow specific amount if 2 specific classes are selected together. . such as $15 off if a registrant registers for 2 specific events together.
Or how can we setup a coupon to only work if the order is over $149.99 (which will be total of 2 classes) - such as $15 discount if 2 classes total is $150.
Please advise.
Thank you.
Mac