、、。
My intense studying was worth it, since I passed the exam.
Literal
Intense-study [even/too-も], entrance-exam [at-に] passed-[because-から], that-amount-[それだけ-possessive-の] value [subject-が] existed.
三 distinct elements. 猛勉強 ('intense studying') is a compound noun where 猛 ('fierce') prefixes 勉強. The も after it means 'even the intense studying [proved worthwhile].' ~だけの is a useful frame for 'of that extent, corresponding to that,' often translated as 'worth the effort.' 受験に受かる ('pass an exam') takes に to mark the target of the passing.