Answer : B. line 3
5(x-5)=15 ----> 1
We remove the parenthesis by distributing 5 inside the parenthesis.
5x - 25 = 15 ----> 2
To get rid of -25, add 25 on both sides
5x - 25 + 25 = 15 + 25 ----> 3
5x = 40 ----> 4
Divide by 5 on both sides
x = 8
From the given options we can see that there is a error in line 3.
Instead of adding 25 , they subtracted 25
So line 3 shows the first error.