Speedboat Acceleration Question

[aquapod17]

Homework Statement

A speedboat moving at 31.0 m/s approaches a no-wake buoy marker 100 m ahead. The pilot slows the boat with a constant acceleration of -3.5 m/s2 by reducing the throttle.
(a) How long does it take the boat to reach the buoy?
______ s
(b) What is the velocity of the boat when it reaches the buoy?
______ m/s

Homework Equations

a = (v_f-v_i)/t
v_f = v_i + at
d = v_it + (1/2)at^2
v_f^2 = v_i^2 + 2ad

The Attempt at a Solution

I keep getting an incorrect answer, but this is what I have been doing.
100 = 31t + (1/2)(-3.5)t^2

 

[aquapod17]

Nevermind I got it! How do you delete threads. I feel really bad leaving this up here when I figured it out myself, but I don't know how to delete!

 

[tiny-tim]

Nevermind I got it! How do you delete threads. I feel really bad leaving this up here when I figured it out myself, but I don't know how to delete!

Hi aquapod17!

You can't delete, you can only do a "never mind" post …

but it's ok … lots of members do that …

I think having to type it out for PF actually helps to make the question clearer!