Literally: That was promised not more foolishly than it was foolishly believed, just as if the arts of a soldier and of a general were the same.
Here you can make several improvements; avoid the repetition of foolishly, and use a better term than arts, and perhaps break up the sentence into two short ones. Thus:—
The folly of the promise was not greater than that of the credit it received. Just as though the qualities of a soldier and of a general were the same!
[VI.] Data pro quinque octo milia militum; pars dimidia cives, pars socii.
(i.) Vocabulary.—
dimidia √med-, mid- = middle, so dimidius = dis + medius.
(ii.) Translation.—This sentence is very simple: notice that here, too, sunt and erant are omitted.
Eight thousand soldiers were given him instead of five: half were citizens, half allies.
[VII.] Et ipse aliquantum voluntariorum in itinere ex agris concivit, ac prope duplicate exercitu, in Lucanos pervenit, ubi Hannibal, nequiquam secutus Claudium, substiterat.
(i.) Vocabulary.—