#### Answer

258

#### Work Step by Step

According to the question, July 1 of the base year is represented by $x=0.5$. Therefore, we substitute $x=0.5$ in the equation to find the pollution level y on the aforementioned date:
$y=7(1-\cos2\pi x)(x+10)+100e^{0.2x}$
$y=7[1-\cos2\pi (0.5)](0.5+10)+100e^{0.2\times0.5}$
$y=7(1-\cos \pi)(10.5)+100e^{0.1}$
$y=7[1-(-1)](10.5)+100(1.1052)$
$y=7(2)(10.5)+110.52$
$y=147+110.52$
$y=257.52\approx258$
Therefore, the pollution level on July 1 of the base year is 258.