The average of 4, 9, 16, 25 and x is 2x. what is the value of x? a) 4 b)6 a)9 c)9 d)12

The average of 4, 9, 16, 25 and x is 2x means that;
(4+9+16+25+x)/5=2x
Multiply both side by 5
5(54+x)/5=2x(5)
54+x=10x
Subtract x to both side
54+x-x=10x-x
54=9x
Divided 9 to both side
54/9=9x/9
x=6
Check:
Substitute x with 6
(4+9+16+25+x)/5=2x
(4+9+16+25+6)/5=2(6)
60/5=12
12=12; so x=6 which marks B as the correct answer. Have a nice day!

Ithink is a. true, but not sure

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2