Equation applications: 2 shapes, same perimeter, i need on all questions!

Brent paid for 6 avocados with a $20.00 bill. he received $10.40 in change. construct and solve an equation can be used to find the price , of each avocados

Asix-sided die of unknown bias is rolled 20 times, and the number 3 comes up 6 times. in the next three rounds (the die is rolled 20 times in each round), the number 3 comes up 6 times, 5 times, and 7 times. the experimental probability of rolling a 3 is 10 %, which is approximately % more than its theoretical probability. (round off your answers to the nearest integer.)

What are the solutions of the equation x4 + 6x2 + 5 = 0? use u substitution to solve.