Calculations not working - combo box quantities at different price points

I have written this code for a combo box (qmblu) with the quantities as seen in the formula, but the only value displaying is for qty=1 (I checked by changing the numbers to 1, 2, etc, instead of 12.22 and '1' showed in the price field). Even the else "" is being ignored with default on the first value. Can anyone please tell me what I'm missing? The combo box works - my product of the two fields changes based on quantity changes, but always multiplies by the same price.

I'm not a coder; created this based on Thom Parker's articles, but it makes sense to me...

Thanks!

var qty = this.getField("qmblu").value;

if( qty=1 ) event.value = 12.22;

else if( qty=2 ) event.value = 12.22;

else if( qty=3 ) event.value = 12.22;

else if( qty=4 ) event.value = 12.22;

else if( qty=5 ) event.value = 10.80;

else if( qty=10 ) event.value = 10.44;

else if( qty=20 ) event.value = 10.44;

else if( qty=50 ) event.value = 9.72;

else if( qty=100 ) event.value = 9.36;

else if( qty=200 ) event.value = 9.36;

else event.value = "";