Find the zero of the following function f$.$ Do not use a calculator.

f left parenthesis x right parenthesis equals $1\mathrm{.}5$ x plus $3$ left parenthesis x minus $2$ right parenthesis plus $4\mathrm{.}5$ left parenthesis x plus $7$ right parenthesisf$($x$)=1\mathrm{.}5$x$+3($x$2)+4\mathrm{.}5($x$+7)$

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Part $1$

The zero of the function is

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$($Type an integer or a simplified$$ fraction.$)$