"How tall is that girl?"
Translation:Jak vysoké je to děvče?
I'm not sure I understand what you're asking. But... holka and dívka are grammatically feminine, so would use ta and vysoká. Děvče, being grammatically neuter, gets to and vysoké. If that isn't what you wanted to know, please ask a more specific question.
I wrote "jaka" instead of "jak" because the feminine subject "holka", bit the correct answer says that it should have been "jak". Could someone please explain why "jaka" is not correct?
Jak is the same as English How, there is no feminine or masculine gender for it, it is an adverb (or a conjunction). Adverbs do not have genders.
Jaký/Jaké/Jaké is a pronoun and it does have a gender, but it is a different word.
"Holka" is feminine, "děvče" is neuter. You need to use the correct gender ending.
"Jak vysoká je TA holka?" is accepted. Since holka is feminine, you need ta as the demonstrative.
I think we have to allow the "je to/to je" construction here as well. I will add it.
girl is an English word and it is of course feminine
holka is feminine
dívka is feminine
děvče is neuter
So when I tried it again I answered 'Jak to děvče je vysoké? and was marked incorrect again. So it's just my word order that's incorrect here?
You need an adverb because you are asking for a property of a verb (How tall IS). Jak is such an adverb. The answer can be an adverb: hodně, málo, trochu. She is VERY tall.
Jaký/á/é is a pronoun and it is used to ask for an adjective, for a property of a noun or pronoun (Jaká je ta holka? Je vysoká. She is TALL.).
You are right that an adverb is needed here but not because of the verb "is" -- to be / být governs adjectives. But "jak" here modifies an adjective (jak vysoké, not jak je), and adverbs are used to do that.