Answer
$1$
Work Step by Step
Recall the acronym PEDMAS, which tells us the order of operations:
P: Parenthesis and other grouping symbols (including fraction bars)
E: Exponents
D/M: Division and Multiplication (from left to right)
A/S: Addition and Subtraction (from left to right)
Use the rule above to obtain:
$=\dfrac{16 + 9}{4-(-21)}
\\=\dfrac{25}{4+21}
\\=\dfrac{25}{25}
\\=1$
