Answer:
2 seconds
Explanation:
The variable S represents the height off the ground, so we can substitute in the value 140 for it:
We can add
to both sides and subtract
so the equation is in standard form:
Every term has five as a factor, so we may divide both sides of the equation by 5.
To factor this, we need two numbers that multiply to 28 and sum to -16. These numbers are -14 and -2, so these are the two factors:
We can see that when t = 14 or 2, the whole left has a value of zero, so they are the two answers.
We are asked when the rocket first is at 140m, and 2 seconds is before 14, so the answer is 2 seconds.