In order to calculate the electronegativity of 2 elements, we need to have their individual values of electronegativity, which can be easily found in tables online the values for every element, and for the elements in our question we have:
H = 2.1
F = 4.0
Cl = 3.0
Br = 2.8
I = 2.5
Now we can find the difference of electronegativity:
HBr = 2.8 - 2.1 = 0.7
HF = 4.0 - 2.1 = 1.9
HI = 2.5 - 2.1 = 0.4
HCl = 3.0 - 2.1 = 0.9
