$textbf{(a)}$ The given two waves are having the same phase. Therefore, the resultant wave will have the amplitude as addition of amplitudes of two given waves.

$$
begin{align*}
A_{res} & = A_1 + A_2
end{align*}
$$

The resultant is shown in the given figure.

$textbf{(b)}$ The given two waves are having the opposite phase. Let us assume that both the waves have same amplitude. Therefore, the resultant wave will have zero amplitude. waves.

$$
begin{align*}
A_{res} & = A – A = 0
end{align*}
$$

The resultant is shown in the given figure.

The speed of the first wave and the second wave is given as

$$
begin{align*}
v_1 & = 1.0 mathrm{m/s} \
v_2 & = -1.0 mathrm{m/s}
end{align*}
$$

As time passes the first wave move towards right and the second wave move towards left.

Therefore, the sketch of the resultant wave at $t=1.0$ s is shown in the given figure.

The sketch of the resultant wave at $t=2.0$ s is shown in the given figure.

The sketch of the resultant wave at $t=2.5$ s is shown in the given figure.

The sketch of the resultant wave at $t=3.0$ s is shown in the given figure.

The sketch of the resultant wave at $t=4.0$ s is shown in the given figure.