x+1/5x+1/5x+x=180
x=75
\(x + (1/5) x + (1/5)x + x = 180\\( 2 + (2/5))x =180\\ x = \dfrac{180}{\frac{12}{5}}=\dfrac{5}{12}\times 180 = 5 \times 15 = 75 \)