>>321
本当だ!!

X + X + X = 30

Y + Y + X = 20

2Z + 2Z +Y = 13

X + (Y+2Z) x Z = ?

これはわからん

X=10
Y=5
Z=2

X + (Y+2Z) x Z = 10 + (5+2x2)x2 = 10 + 9x2 = 10 +18 = 28