I'm having a difficulty in understanding the below questions:

(1) Use the natural number series to find the following

(a) The sum of the first n terms in the series (1)(3)(5) + (2)(4)(6) + (3)(5)(7) + ...

(b) $\displaystyle \sum_{r=1}^{2n} r^2$

(c) $\displaystyle (n+1)^2 + (n+2)^2 + ... ... + (2n)^2$

(2) Expand $\displaystyle \frac{6}{p(p+3)} $ into partial fractions

(a) Use the above result to find $\displaystyle \sum_{r=1}^{n} \frac{6}{r(r+3)} $

(b) Hence find the value of $\displaystyle \frac{1}{4} + \frac{1}{10} + \frac{1}{18} + \frac{1}{28} ... $