Jay Garrick is the time remnant of the Zoom. To explain this, I first need to explain the time remnant. Time remnant of the speedster means he is from that timeline which got changed. Suppose Zoom traveled back in the time where he has already become Speedster.
He Can't Be Two Places At Once So, as he explained to the entire team in the most recent episode, "Versus Zoom," he needed to find a way to be in two places at once: the answer was a time remnant, retrieved from the past.
Third, Jay Garrick is the original Flash from DC Comics. On the TV show, he was able to catch up to Barry Allen in the Speed Force (to try to stop him from changing the timeline), but he was beaten by Savitar. He was also beaten by Zoom, so he's not as fast as others.
When Zoom defeated The Flash" of Earth-3, Jay Garrick, he imprisoned Jay in the lair and outfitted him with a speed-dampening mask. Zoom interrogating Jesse. After Zoom abducted Harrison Wells' daughter, Jesse Wells, from her college, he imprisoned her in a cell in this station.
When Jay first became fast, he made no attempt to hide his powers. His doctors knew about them, both football teams knew about them, and in Flash Comics #3, everyone knows his identity. The second Flash, Barry Allen, used a similar trick in Flash #218 to hide his identity when he was unmasked.
Consequences of time travel. Jay greets Barry in 1998. During his stay on Earth-2 Harry informed Jay, still confused as to why Barry was especially shocked to see him, that Jay's Earth-1 doppelgänger was Henry Allen, Barry's deceased father.
A carefully filled measuring cup should weigh 8.0 oz or 227 grams. 2 cups should weigh 16.0 oz or 454 grams. 3 cups should weigh 24 oz 680 grams. 4 cups should weigh 32 oz or 907 grams.
2 cupsHow Many Cups of Chocolate Chips in 6 oz? 24 oz? 36 oz? 72 oz?Oz of Chocolate Chips (Weight)Cups of Chocolate Chips (Volume)12 oz2 cups chocolate chips24 oz4 cups chocolate chips36 oz6 cups chocolate chips72 oz12 cups chocolate chips
18 oz = 2.25 cups Thus, you can divide 18 by 8 to get the same answer.