Let Planet 2 = X
Planet 1 = X + 31.3
Planet 3 = x +(31.3+23.2) = x + 54.5
Add the 3 distances together:
x + x +31.3 + x + 54.5 = 193.8
3x + 85.8 = 193.8
Subtract 85.8 from each side:
3x = 108
Divide both sides by 3:
x = 108 / 3
X = 36
Planet 2 = 36 million miles
Planet 1 = 36 + 31.3 = 67.3 million miles
Planet 3 = 36 + 54.5 = 90.5 million miles
36 + 67.3 + 90.5 = 193.8