1. x (spam) = 2y (normal mail) + 4

2. x + y = 79

therefore making a simultaneous equation putting the first expression into the second

2y + 4 + y = 79

3y + 4 = 79

3y = 79 - 4

3y = 75

y = 25

if y = 25

x = 79 - 25

x = 54

therefore 25 normal mail, 54 spam