When simplifying a fraction, whatever you do to the top has to be the same as what you do to the bottom. if nicholas simplified the numerator by 5 he has to simplify his denominator by 5. if did that correctly, 20/5=4 and 30/5=6. however, he can still simplify. taking the new fraction 4/6 you can divide both the numerator and denominator by 2. 4/2=2 and 6/2=3. nicholas would now have the fraction 2/3
(4x+5)(4x-5) is equal to 16x^2+20x-20x-25 The positive and negative 20x cancel out Leaving you with: 16x^2 - 25 [S/N this is a pattern that shows up a decent amount. Whenever you have something that looks like (x^2-y^2) it factors out to (x+y)(x-y). It might be helpful to remember]
The next one, (4x+5)2, just follows the distributive property. Multiply both components within the parentheses bye the coefficient of 2: 8x+10