For triangle, ARST , the length of side RS is 5x^3- 7x² +9, the length of side ST is x^3 - 5r^2? +1 and the length of side RT is 9x^3- 5. What is the perimeter of triangle RST?

Problem number 26 of the rhind papyrus says: find a quantity such that when it is added to of itself the result is a 15. the modern day equation that models this problem is x + x = 15. what is the solution to the equation? x = 10 x = 12 x = 15 x = 30