Answer
$-24$
Work Step by Step
The order of operations follow the following hierarchy (PEMDAS rule):
(i) Parentheses/grouping symbols
(ii) Exponents
(iii) Multiplication/Division, whichever comes first from the left
(iv) Addition/Subtraction, whichever comes first from the left
Use the rule above to obtain:
$=3(4)-4(9)
\\=12-36
\\=-24$