Which equation can be used to find the value of x if the shortest side, y, measures 2.1m

Perimeter of an Isosceles triangle =  7.5 m
Shortest side = 2.1 m 
Now,
We know, the other two sides in an isosceles triangle are equal to each other. 
So,
the other two sides are going to be equal to "x"

Now,
Perimeter = Sum of all sides
7.5 m = 2.1m + x + x
2x =   7.5 m - 2.1 m   <--- you are going to have to use this equation                                                  to find the values of x
x = 5.4 m / 2
x = 2.7 m

So, the other two sides are equal to 2.7m