Using the splitting middle term - the middle term of the general equation is divided in two such values that:

Product = a.c

For the given equation a = 4; b = -9 ; c = -100

= 4. - 100 = - 400

And either of their sum or difference = b

= - 9

Thus the two terms are - 25 and 16

Difference = - 25 + 16 = - 9

Product = - 25.16 = - 400

x(4x-25) + 4(4x-25) = 0

(4x-25)(x + 4) = 0

(4x-25) = 0 or (x + 4) = 0

x = 25/4 or x = -4

Roots of equation are 25/4, - 4