AND OPERATOR

I have a simple DAX formula that i want to use to distinct count the number of customers who have met a certain criteria. I have a table that defines these criteria i.e Tiers I am doing this on power bi and this is the measure that i am using;

MTierB = 
var y = SUM('Brand Tiers'[TierB]),
var x = SUM('Brand Tiers'[TierA]) 
return CALCULATE(DISTINCTCOUNT('Sales By Customers'[CUSTOMER_StoreCode]), KEEPFILTERS(FILTER('Sales By Customers', 'Sales By Customers'[Total Sales in MSU] >= y AND <=x )))

I am getting a syntax error. The AND operator is underlined in red and i dont understand why? Please help out