Answer: かく (To Write) is already in the present affirmative form, but in plain, informal form. If you are trying to make the verb for かく formal, it would conjucate to "かきます" (書きます).
Explanation: When you have the informal present-affirmative version on a verb, (also known as the dictionary form) and you want to make it formal, you first have to conjugate the verb. There are two types of verbs; the "る" verbs (Verb Ends With a "る" Sound), and the "う" verbs (Verb Ends With a "う" Sound), though, some are exceptions, and some are a bit different. Whenever you have a "る" verb, all you do is get rid of the "る," and add "ます" at the end for the formality.
Examples:
たべる -----> たべます / To Eat
ねる -----> ねます / To Sleep
Whenever you have an "う" verb, what you have to do is replace the "う" sound of the verb to an "い" sound. Then you have to add the ます for formality.
Examples:
やすむ -----> やすみます / To Rest
あそぶ -----> あそびます / To Play
いう -----> いいます / To Say
NOTE: You still have to be careful, because there are some verbs in Japanese that don't follow this conjugation rule. Hope this helps!
