Answer:
Step 2 involved distributive property and the value of y is equal to 8.
Step-by-step explanation:
In step 2, there has been an error in applying the Distributive Property correctly.
Distributive Property- a(b+c)
= a x b + a x c
Step 2: 
Step 3:
Step 4: 
y=8
What is your first expression? because i can not answer without the first expression.
Perimeter of triangle= 81
x+3x-1+4x-2=81
8x-3=81
8x=84
x=10.5 so sides are 10.5,30.5,40.