Allen score in the video game was changed by -75 points because he miss some targets he got -15 points for each miss target how many targets did he miss

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