Answer
a) $16%$, b)$29
Work Step by Step
a) Typical percentage problem:
What percent ($n$, as a decimal number) of (the base amount $y$) is $x?$
Translated:$\quad n\cdot y=x$
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Here, What percent ($n$, as a decimal number) of ($y=25$) is ($x=4$)$?$
Translated:$\quad n\cdot 25=4$
... divide with $25$
$ y=0.16\qquad$ .... convert to percent notation,
( move the decimal point two places to the right and write a percent symbol.)
$=16\%$
b) $25+4=\$ 29$