quest. 4 in Q&A

[teomas9212693]

I'm confused about when it's appropriate to use sin and cos functions. An example question is listed below which came from Chapter 3 Q&A.

Approximately what magnitude a force would have to be applied in addition to the frictional force in order for the block in experiment 1 not to move on surface 3 when the plane is 60° to the horizontal? (note: sin 60 = 0.87; cos 60 = 0.5)

[DLBMCAT]

Me too, any help here would be greatly appreciated. Oh, and I read the chapter in the book and still need help!