Answer:
Given the system of equation:
......[1]
......[2]
we can rewrite equation [2] as;
......[3]
Substitute equation [3] into [1] to eliminate x, and solve for y;

Using distributive property: 

Combine like terms;
16 - 8y = -4
Add 4 to both sides we have;
20 - 8y = 0
Add 8y to both sides we have;
20 = 8y
Divide 8 to both sides we have;

Substitute the y-value in [3] we have;

x = 8 - 5 = 3
Therefore, the expression should be substituted into the first equation is,
and also the value of x = 3 and y = 2.5
Radical 2 = 1.4 So 1.4 * 6 = 8.4
a^2 + b^2 = c^2
8.4^2 + 8.4^2 = square root of c
70.56 + 70.56 = 141.12 ≈ 141
Then you must find the square root of 141 which is 11.874 ≈ 11.9
Side a = 8.4
Side b = 8.4
Side c = 11.9