75 supermarkets are surveyed to determine which brands of detergent they sell. All sell at least one of brands A, B, or C. 55 sell brand A, 57 sell brand B, and 50 sell brand C. 33 supermarkets sell both A and C, while 17 supermarkets sell both A and B but not C. 22 supermarkets sell all three brands. Construct a Venn diagram which represents this situation. Use this diagram to determine how many supermarkets sell: a) both A and C but not B
b) at least two of these brands.