Question 158117
Let x=supplementary angle



Since x and f are supplementary, this means that the two angles add to 180 like this:


{{{x+f=180}}}



{{{x+78=180}}} Plug in {{{f=78}}}



{{{x=180-78}}} Subtract {{{78}}} from both sides.



{{{x=102}}} Combine like terms on the right side.



So the supplementary of angle f is 102 degrees



Note: 


102+78=180
180=180