77 Grk “He”; the referent (the man) has been specified in the translation for clarity.
78 Grk “How am I able, unless …” The translation is based on the force of the conjunction γάρ (gar) in this context. The translation “How in the world can I?” is given in γάρ 1.f.

In other versions

And he said, “How can I, unless someone guides me?” And he invited Philip to come up and sit with him.

“How can I,” he said, “unless someone explains it to me?” So he invited Philip to come up and sit with him.

“How can I,” he said, “unless someone guides me?” So he invited Philip to come up and sit with him.

The man replied, “How can I, unless someone instructs me?” And he urged Philip to come up into the carriage and sit with him.

And he said, “So how could I, unless someone will guide me?” And he invited Philip to come up and sit with him.

And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him.

Public Domain