Given: $q_1=+2.5\times10^{-7}$ C at $(0,0,-15\text{ cm})$, $q_2=-2.5\times10^{-7}$ C at $(0,0,+15\text{ cm})$. Separation $=30$ cm $=0.3$ m.

(a) Dipole moment magnitude:

$$p=q\times d=2.5\times10^{-7}\times0.3=7.5\times10^{-8}\text{ C m}$$

Direction: from negative charge ($q_2$ at $+z$) to positive charge ($q_1$ at $-z$), i.e. along the $-z$ direction.

So $\vec p = -7.5\times10^{-8}\ \hat k$ C m.

(b) Field at origin (equidistant from both charges, $r=0.15$ m each):

Due to $q_1$ (positive, at $z=-0.15$): field points away from it, i.e. along $+\hat k$, magnitude $\dfrac{kq_1}{r^2}=\dfrac{9\times10^9\times2.5\times10^{-7}}{(0.15)^2}=1\times10^5$ N/C

Due to $q_2$ (negative, at $z=+0.15$): field points towards it, i.e. also along $+\hat k$, same magnitude $1\times10^5$ N/C

Both add up:

$$E_{net}=1\times10^5+1\times10^5=2\times10^5\text{ N/C, directed along }+z\text{ axis}$$