Find the magnitude of the horizantal force

[dg_5021]

Hey can someone please help me with this problem. accorning to the back of the book the answer is 28N. I tried doing this first multipling 1.41*7.5 = 10.575. Then i used this formula 10.575cos(13)= but i got 9.59625.
Am I missing a step, please help?

Problem:
a shopper pushes a 7.5-kg shopping cart up a 13 incline. Find the magnitude of the horizantal force, F, needed to give the cart an acceleration of 1.41 m/s2.

[dg_5021]

someone please help?

[Tide]

You need to account for the fact that gravity is tending to accelerate the shopping cart downhill. :-)