One and three-fourths written as an improper fraction is 7/4.
Now we multiply 4/5 by 7/4. The '4' in each fraction cancels out the '4' in the other fraction, so that we are left with (1/5)(7/1), or 7/5 (improper fraction), or 1 2/5 (mixed number)
I just graphed this equation, and it shows that the projectile will hit the ground at 5.3 seconds. I could be wrong but I'm going with the calculator is right I hope. I hope this helps you!