Algebra is very confusing to me...Plss Help Me before I pull my hair out! 42x^3 divided by 2x Solve the equation and explain your answer

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