The board unanimously agreed to assent ____ the revised budget proposed by the finance committee.

Assent to something: 
English Meaning - To agree to or give official approval to something. 
Bangla Meaning - সম্মত হওয়া। 
Example Sentence - Eventually, the government assented to a modified version of the plan.

So, Complete Sentence - The board unanimously agreed to assent to the revised budget proposed by the finance committee. 
Meaning - অর্থ কমিটির প্রস্তাবিত সংশোধিত বাজেটে বোর্ড সর্বসম্মতিক্রমে সম্মত হয়।

আরো কিছু Appropriate Prepositions, 
Akin to - সদৃশ; 
Allot to -বরাদ্দ; 
Appetite for - ক্ষুধা। 

Source: 
1. Cambridge Dictionary. 
2. Accessible Dictionary by Bangla Academy.