Split the thing up into 3 bits. I'm leaving out the units (metres, seconds, etc.) for clarity, but be aware your teacher will crucify you if you do the same.
1. You have a = 0.3, u = 0, t = 90. From that you can easily calculate the distance by (which you did, whether you got the right answer depends on how accurately you punched your calculator keys). Now, what you *also* want to do is get the velocity at this point - so use for that (and you know u = 0 and a = what I said above.
2. Now you know how fast it's going, and you've got a = 0 so and that gives you the second distance.
3. In this case, you have again, but this time , u is the velocity from the last bit, and . Then rearrange the equation so it's in terms of s.
Add them up together and you're done.