Answer: 
Step-by-step explanation:
Least Common Multiple :The least positive number that is a multiple of two or more numbers.
To find : The least common multiple of:
and 
Since, 

The least common multiple of:
and
=
[take highest power of x and y ]
Hence, the least common multiple of:
and
= 
Add all sides together to find the length of each side
The formula for the circumference of a circle = 2 x radius x pi
The radius is given as 21 cm and pi = 3.142
Circumference = 2 x 21 x 3.142 = 131.964 cm
Answer: x=-2
Y= -20
Step-by-step explanation
You replace the y in the second equation with 10x. This is because it says 10x=y
2x+10x=12x so you put that
12x=-24
To get x by its self you divide by 12.
-24 divided by 12 is -2.
Now you plug in -2 to either equation as y. I chose the first one because it's easier.
10(-2)=y
-20=y