Find the value of each variable in the parallelogram​

An arrow is shot vertically upward at a rate of 180ft/s. use the projectile formula h=−16t2+v0t to determine at what time(s), in seconds, the arrow is at a height of 420ft. round your answer(s) to the nearest tenth of a second.

Its worth 10000000 points need asap if you answer correctly ill mark brainliest

What is the missing step in this proof ?