Greta Thunberg, the 'expert', only gave you ten in 2018.
Quote:
Delta-v
Delta-v, symbolized as ∆v and pronounced delta-vee, as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as launching from or landing on a planet or moon, or an in-space orbital maneuver.Wikipedia
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I guess it's hyphenated. Sorry for the confusion.