He already has 25 and he collects 2 cards every month.
In x month, he would have
X = 25 + 2x amount of cards
For instance, in 4 months, he would have
X = 25 + 2(4) = 25 + 8 = 33 cards
25 in the equation is a constant since he already has that in stock before considering or calculating what he gets monthly to increase his number of cards.
So distribute using distributive property a(b+c)=ab+ac so
split it up (5x^2+4x-4)(4x^3-2x+6)=(5x^2)(4x^3-2x+6)+(4x)(4x^3-2x+6)+(-4)(4x^3-2x+6)=[(5x^2)(4x^3)+(5x^2)(-2x)+(5x^2)(6)]+[(4x)(4x^3)+(4x)(-2x)+(4x)(6)]+[(-4)(4x^3)+(-4)(-2x)+(-4)(6)]=(20x^5)+(-10x^3)+(30x^2)+(16x^4)+(-8x^2)+(24x)+(-16x^3)+(8x)+(-24) group like terms [20x^5]+[16x^4]+[-10x^3-16x^3]+[30x^2-8x^2]+[24x+8x]+[-24]=20x^5+16x^4-26x^3+22x^2+32x-24