Let us draw Venn diagram.
From statement (1),
(b + c) - (b + e) = 8
⇒ c = 8 + e ... (1)
From statement (2),
(a + b) - (d + e) = 7
⇒ a + b = 7 + d + e ... (2)
From statement (3),
(a + b + e + f) - (b + c) = 21
⇒ a + e + f = 21 + c
⇒ a + e + f = 21 + 8 + e [From equation (1), c = 8 + e]
⇒ a + f = 29 ... (3)
From statement (4) ,
(a + b + e + f) + (d + e) = 66
⇒ a + b + d + 2e + f = 66 ... (4)
From statement (5),
b + e = 21 ... (5)
⇒ c = 21 - 4 = 17 ... (6)
From equation (1),
e = c - 8 = 17 - 8 = 9 ... (7)
From equations (5) and (7),
b = 21 - e = 21 - 9 = 12 ... (8)
From equations (3) and (4),
b + d + 2e = 37
⇒ d = 37 - 12 - 2 x 9 = 7 ... (9)
From equations (2), (7), (8) and (9),
a + b = 7 + d + e
⇒ a = 7 + 7 + 9 - 12 = 11 ... (10)
From equations (3) and (10),
a + f = 29
⇒ f = 29 - 11 = 18
Number of friends who only watched movies = 7