Chi-Squared Goodness-of-fit-test

Please help me solve this problem

EDUCATION EXPERTS CONDUCT A STUDY OF A COURSE PERFORMANCE DISTRIBUTION AFTER THE GRADES HAVE BEEN POSTED . THEY ASSUMED THE GRADE DISTRIBUTION SPECIFIED IN THE ROW TITLED " PROBABILITY " BELOW GRADES A 1 C I W TOTAL OBSERVED FREQUENCY 60 90 210 75 45 THE 5010 PROBABILITY 0.15 0.20 0.35 0. 15 0.10 0 05 100 EXPECTED COUNTD. AT THE 5% SIGNIFICANCE LEVEL, DO YOU HAVE ENOUGH EVIDENCE TO CONCLUDE THAT THE GRADE DISTRIBUTION DIFFERS FROM THE HYPOTHETICAL PROPORTIONS? SPECIFY THE FOLLOWING ELEMENTS OF YOUR DECISION MAKING PROCEDURE. CRITICAL VALUE = DECISION: (REJECT) - OR - (DO NOT REJECT) THE NULL HYPOTHESIS REJECTION RULE: WHY DO YOU REJECT OR NOT REJECT