There exists so many properties of multiplication and addition in algebra. There are the communitative properties for both, associative properties, distributive property, identity properties, etc.
In this item, we are given with,
5 x (3x + y) = 5 x (3x + 1y)
What is different between the terms in the left-hand side and the right-hand side of the equation is that y in the right-hand side of the equation is multiplied by 1 making it 1y.
This property of multiplication is called the MULTIPLICATIVE IDENTITY PROPERTY wherein 1 is used as the multiplier.
