How many terms are in the expression 10x? !

Can someone explain the elimination method to me for this problem?

The probability that a college student belongs to a health club is 0.3. the probability that a college student lives off-campus is 0.4. the probability that a college student belongs to a health club and lives off-campus is 0.12. find the probability that a college student belongs to a health club or lives off-campus. tip: p(a or b) = p(a) + p(b) - p(a and b) 0.54 0.58 0.70 0.82

Asequence is defined recursively using the formula f(n + 1) =f(n) - 5. which sequence could be