First, combine like terms on the left side of the equation:
#4f - color(red)(5) + color(red)(6) = 35#
#4f + 1 = 35#
Next, subtract #color(red)(1)# from each side of the equation to isolate the #f# term while keeping the equation balanced:
#4f + 1 - color(red)(1) = 35 - color(red)(1)#
#4f + 0 = 34#
#4f = 34#
Now, divide each side of the equation by #color(red)(4)# to solve for #f# while keeping the equation balanced:
#(4f)/color(red)(4) = 34/color(red)(4)#
#(color(red)(cancel(color(black)(4)))f)/cancel(color(red)(4)) = (color(red)(cancel(color(black)(34)))17)/color(red)(color(black)(cancel(color(red)(4)))2)#
#f = 17/2#