Let a = weight of large box in pounds
Let b = weight of small box in pounds
(1) 65a + 55b=4425
(2) a+b=75
Now we can simultaneously solve these equations.
a = 75 - b. Hence 65(75 - b) + 55b = 4425 So 4875 - 10b = 4425 and 450 = 10b hence b = 45.
SImilarly a = 30. Now we can verify too by putting in the calculated values.