I'm not sure what I'm missing in my calculations, I keep getting stuck.

Proportions of annual sales: 50, 30, 11, 9, percent.

Surveying: 1000 people in a city.

Store frequencies (for purchasing):

#1: 510

#2: 300

#3: 120

#4: 70

How do i find the expected cell frequency for store #1? And how do I find the chi-sq statistic?

Thanks a lot.