The other number is 3! Hope this helps :)
Set h to 640 and solve for t:
640 = -490t^2 + 1120t
Subtract 640 from both sides:
-490t^2 + 1120t - 640 = 0
The formula to solve a quadratic equation is:
x = -b -/+ sqrtroot (b^2-4ac)/(2a) where a = -490, b = 1120 and c = -640
Solve:
x = -1120 -/+ sqrtroot (1120^2-4(-490)(-640) )/ 2(-490)
x = 8/7 = 1.1428 = 1.14
Time was 1.14 seconds
3x + (x+3) = 19
4x + 3 = 19
4x = 16
x = 4
y= x+3
y= 4+3
y= 7
Answer: $0.28
Step-by-step explanation: Pic is attached. Hope this helps. Sorry for the bad handwriting, I'm writing with a mouse.