nilai x + y - z mohon dibantu

semoga membantu ya.. maaf kalo slah

cari yg didalam segitiga dulu....
40 = y + 10
30 = y
cari yg diluar segitiga
130 = 2x + 40
90   = 2x
45   = x

80 = 3z + 20
60 = 3z
20 = z

Thats mean

x + y - z = 45 + 30 - 20 = 55