Pulling masses up a tilted plane with kinetic friction

[jamiebean]

Homework Statement

attached below

Relevant Equations

N= mg

first, i calculated the kinetic friction:
0.77 x (weight of the 2 boxes x 9.8)= 55.16N

then i calculated the angle of the triangle:
tan^-1(2.5/4.75)=27.758

then i drew this

then i used sine to find out force 3 which is 33.3556

so the final force needed is 33.3556 + kinetic friction= 88.516

is this correct?

 

[kuruman]

My numbers disagree with yours. Since you do not provide the equations in which you substituted the numbers, I cannot check the details of where you went wrong. The statement

then i used sine to find out force 3 which is 33.3556

is not informative enough. Please post a more complete solution.