Style Strike --- Can you use two on the same attack?

[Barachiel Shina]

By 15th level, an Unchained Monk can use 2 style strikes per round when flurrying.

Can you make the two strikes in the same attack? For example, Hammerblow and Shattering Punch in one attack? Or do they have to be separate attack rolls?

[logan grayble]

From the PFSRD:

"At 15th level, he can designate up to two of his unarmed strikes each round as a style strike, and each one can be a different type. The monk can choose from any of the following strikes."

Sounds like two different attacks to me.