Equation 3:

2x2 + 7x + √36 = 0
2x2 + 7x + 6 = 0
2x2 + 4x + 3x + 6 = 0
2x(x + 2) + 3(x + 2) = 0
(x + 2)(2x + 3) = 0
x = -2, -3/2
Equation 1: ax2 + bx + 4 = 0
Equation 2: ax2 + 3x + c = 0
Now, Equation 1 + Equation 2 = Equation 3
So, ax2 + bx + 4 + ax2 + 3x + c = 2x2 + 7x + 6
2ax2 + (b + 3)x + (4 + c) = 2x2 + 7x + 6
Here, 2a = 2 => a = 1
b + 3 = 7 => b = 4
4 + c = 6 => c = 2
Now, Equation 1:
ax2 + bx + 4 = 0
x2 + 4x + 4 = 0
x2 + 2x + 2x + 4 = 0
(x + 2)(x +2) = 0
x = -2, -2
And Equation 2:
x2 + 3x + 2 = 0
x2 + 2x + x + 2 = 0
(x + 2)(x + 1) = 0
x = -2, -1
a + b + c = 1 + 4 + 2 = 7