Answer:
Equation : 100 + (n - 20) × 3.5 = 345
90 students went for tour.
Step-by-step explanation:
Since, the cost of first 20 students is fix and it is $100
and, each student after these 20 students has to pay $3.50, also tour cost is $345.
Let the number of total student went for tour be "n".
Hence, we get equation,
100 + (n - 20) × 3.5 = 345
⇒ (n - 20) × 3.5 = 345 - 100
⇒ (n - 20) × 3.5 = 245
⇒ (n - 20) = 245 ÷ 3.5
⇒ (n - 20) = 70
⇒ n = 90 students