PLEASE HELP!! Directions: Find the sum for each of the following arithmetic series below. Use the summation formula to find the sums.

1. Find the sum of the first 21 terms in a series where a = 20 and t21= 400.

2. Find the sum of the first 100 terms in a series where a = 0 and t100= 99.

3. Find the sum of the first 50 terms in a series where a = 4 and t50= 196.

Acoffee shop orders at most $3,500 worth of coffee and tea. the shop needs to make a profit of at least $1,900 on the order. the possible combinations of coffee and tea for this order are given by this system of inequalities, where c = pounds of coffee and t = pounds of tea: 6c + 13t ≤ 3,500 3.50c + 4t ≥ 1,900 which graph's shaded region represents the possible combinations of coffee and tea for this order?

Given that sin∅ = 1/4, 0 < ∅ < π/2, what is the exact value of cos∅? a. (√4)/4 b. (√15)/4 c. (4π)/2 d. (4√2)/4

What is the circumference of a circle with an area of 50.24 cm²?