Question 1051765
Quadratic equation formula:
ax^2+bx+c = 0
With your numbers:
5a^2+4a = 8 subtract 8 on both sides
5a^2+4a-8 = 0
divide all sides by 5:
x2+0.8x-1.6 = 0 
x = -(0.8÷2)+√(0.8÷2)2+1.6 = -0.4+1.32664991614 = 0.926649916142
or
x = -(0.8÷2)-√(0.8÷2)2+1.6 = -0.4-1.32664991614 =  -1.72664991614