The following provides data for an economy in a certain year. Consumption expenditures $50 Imports $40 Government purchases of goods and services $20 Construction of new homes and apartments $30 Sales of existing homes and apartments $40 Exports $50 Government payments to retirees $10 Household purchases of durable goods $20 Beginning-of-year inventory $10 End-of-year inventory $20 Business fixed investment $30 Given the data, compute the value of GDP.