Determine the structure of the abelian group G defined by generators {a,b} and relations 2a + 4b = 0 and 3b = 0. Do the same for the group with generators {a,b,c,d} and relations 2a + 3b = 4a = 5c + l ld = 0 and for the group with generators {a,b,c,d,e} and relations {a - 7 b + 14d - 21c = 0; 5a - 7 b - 2c + 10d - 15e = 0; 3a - 3b - 2c + 6d - 9e = 0; a - b + 2d - 3e = 0).