Answer:

Step-by-step explanation:
-5+2(10b-2)=31
Expand brackets.
-5+20b-4=31
-9+20b=31
Add 9 on both sides.
20b=40
Divide both sides by 20
b=2
Its a type of thermal expansion and described by fractions that represents the fractional increase length of a thin beam of a material exposed to its temperature increase of one degree celcious,"
X-13=42
x is the "variable", you're taking 13 away from that, and the answer is also given, 42.
I hope this helps you
y=x^2-81
x^2=y+81
x=square root of y+81
f^-1 (x)= square root of x+81