ok so since the total measurement is 180° and you know that 1 of the sides is 40° and the other 2 are the same you will just need to subtract 40 from 180 and split that in half
here's the formula
[tex](180 - 40) \div 2 = \\ 140 \div 2 = \\ 70[/tex]
therefore
x=70°
