#### Answer

Both problems are sums involving common denominators.
To add fractions or rational expressions with the same denominator,
add numerators and place the sum over the common denominator.
Fractions: $\displaystyle \frac{3}{8}+\frac{1}{8}=\frac{4}{8}$
Rational expressions: $\displaystyle \frac{x}{x^{2}-1}+\frac{1}{x^{2}-1}=\frac{x+1}{x^{2}-1}$
Also, both problems have common factors in the numerators and denominators. Both can be reduced:
Fractions: $\displaystyle \frac{4}{8}=\frac{4}{4\times 2}=\frac{1}{2}$
Rational expressions: $\displaystyle \frac{x+1}{x^{2}-1}=\frac{(x+1)}{(x+1)(x-1)}=\frac{1}{x-1}$