You have $15.00 and each shirt you bought was $4.25
$4.25x3=$12.75
$15.00-$12.75= $2.25
So your shorts were $2.25
Then the probability is
P(a)+P(b)-P(a&b)
0.5+0.3-0.5*0.3=0.8-0.15=0.65

$\sec x=\frac1{\cos x}$
$\therefore \cot^2x\cdot\sec^2x= \frac{\cos^2x}{\sin^2x}\frac{1}{\cos^2x}=\frac{1}{\sin^2x}$