已知5個數8,12,15,2x+1,9的算術平均數是13，求x的值

已知5個數8,12,15,2x+1,9的算術平均數是13，求x的值
(8+12+15+2x+1+9)/5=13
45+2x=65
2x=20
x=10

[8 +12 + 15+ (2x+1) +9] /5 =13 <------平均數是13
44 + 2x +1= 13*5
2x = 65-45
2x = 20
x=10

[8 + 12 + 15 + (2X +1) + 9]/5 = 13
8 + 12 + 15 + (2X +1) + 9 = 13x5
44 + (2X + 1) = 65
2X + 1 = 65 -44
2X = 21 - 1
X = 20/ 2
X = 10

8+12+15+(2x+1)+9=13*5
45+2x=65
45+2x-45=65-45
2x=20
x=10

15!!!!!!!!!!!!!!!