this is the example given by my instructor but I don't understand how she got her answer for number 3.

In order to start the block sliding, a horizontal force, F, of 3lb must be applied. What is the coefficient of friction between the block and the surface? Show your calculation. - see Fig 5-8 on pg 101 3. At what angle, , would the surface in question 2 need to be inclined so that the block would just begin to slide? Show your calculation. - see Fig 5-8 on pg 101 u=tan u=F/W=0.1 0.1=tan =tan1(0.1) =5.7 degrees