x-(239+211)=3100:155

x = 470

Steps:

• 239 + 211 = 450
• 3100 : 155 = 3100/155 = 20
• So x − 450 = 20 ⇒ x = 470

(If ":" is read as a ratio, 3100:155 simplifies to 20:1, still giving x = 470.)