Hello :
<span>2x+4y=38 ...(1)
10x+3y=105....(2)
-10x-20y = - 190
10x+3y =105
add : -17y = - 85
y = 5
subsct in (1) : 2x +20 =38
2x = 18
x=9
</span>
<span>they are simply different numerical expressions of the same value</span>
We see a right triangle here.
Use the Pythagorean Theorem:
a^2+b^2=c^2
a & b=legs
c=hypotenuse
a^2+15^2=20^2
a^2+225=400
a^2=175
a=13.2287565553
a=13.2
The missing side is 13.2cm