$$ (5-2i)(3+3i)=a+bi $$

In the equation above, \(a\) and \(b\) are real numbers and \(i=\sqrt{-1}\). What is the value of \(a\)?

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$$ (5-2i)(3+3i)$$ $$ =5(3)+5(3i)-2i(3)-2i(3i) $$ $$ =15+15i-6i-6i^2 $$ $$ =15+9i-6(-1) $$ $$ =15+9i+6 $$ $$ =21+9i $$ $$ \colorbox{aqua}{$21$}+9i=\colorbox{aqua}{$a$}+bi $$