There is a change of base formula for changing per unit impedance from an old base to a new base. What I show below is from the "Electrical and Computer: Power Reference Handbook Version 1.1.2" top of page 35, the supplied cheat sheet/book for the Power PE test.
The following equation may be used to change a per-unit impedance from an old base to a new base:
$$ Z_{\rm new}
= Z_{\rm old} \cdot
\left( {\rm Base}\, kV_{\rm old} \over {\rm Base}\, kV_{\rm new} \right)^2 \cdot
\left( {\rm Base}\, kV\!A_{\rm new} \over {\rm Base}\, kV\!A_{\rm old} \right). $$
You'll notice since voltage base remains constant, the first parenthesis in the change of base formula goes to 1 and can be ignored.
You've listed 98km for this problem but then list the per unit impedance. We normally use the distance to find the total line impedance, which we divide by a calculated "Base Impdance" derived from our base voltage and power to finally get our per unit impedance.
I will re-write the given per unit line impedance of the 98KM line (0.768 + 4.823i) x 10^-3 as (0.000768 + 0.004823i)
Given that the old base is 115MVA = 115,000 KVA and the new base is 1,047MVA = 1,047,000 KVA, we can solve the equation.
$$
\begin{aligned}
Z_{\rm new}({\rm p.u}) &= {\rm New\ Per\ Unit\ Impedance} \\
&= (0.000768 + 0.004823\,i) \cdot 1^2 \cdot \left( 1,\!047,\!000 \over 115,\!000 \right) \\
&= 0.0073 + 0.046\,i.
\end{aligned}
$$
