Círculo área y perímetro

me podrían ayudar no soy para nada buena con esto
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Tom wants to order tickets online so that he and three of his friends can go to a water park the cost of the tickets is 16.00 per person there is also a 2.50 one-time service fee for ordering tickets online write an expression in term of n that represents the cost for n ordering tickets online

Hardest math question of all time can you solve the equation. check for extraneous solutions.9∣9-8x∣ = 2x+3

Write the percent as a fraction or mixed number in simplest form. 0.8%