How is (x-1)(x+4)(x-3)>0 solved?

first solve it with an equal sign

It is zero when
x = -4
x = 1
x = 3
Now graph it in between those points to see where it is +
in fact
for large negative x, your function is negative
so it is + from -4 to 1
then it is negative from 1 to 3
then it is + for x greater than 3