STEP 1:
Find total number of questions on the test. The percent (84%) is out of 100%. So set up a proportion. 84% out of 100% is 63 out of x (total number of questions on the test).
x= total # questions on test
63/x= 84%/100%
cross multiply
(63*100)= (x*84)
6300= 84x
divide both sides by 84
75= x (total # on test)
STEP 2:
Subtract number correct from total number of questions to equal number incorrect.
x= number incorrect on test
x= 75 - 63
x= 12 incorrect answers
ANSWER: 12 incorrect answers
Hope this helps! :)