The first number is 15. The 2nd number is 30 cuz it’s double the first. The third number is 18 less than 30 so it is 12. They all add up to 57. Third # = 12
7 - 2 5/7
= 7 - 19/7
= 49/7 - 19/7
= 30 / 7
= 4 2/7
Equation: 4x+15=31
I have included a picture of my work since explaining might be difficult but the way I solved this if the beginning of algebra and I hope it makes sense.
Your welcome, Katy