Question

I need this written as a proportion (equation involving 2 fractions) so I can solve the equation.

Answer 1

You can set up a proportion like this:

$\frac{1500}{12} = \frac{100000}{x}$

Notice how the samples are represented in the numerator and the defective iPhones in the denominator.  Since you don't know the number of defective iPhones in the 100,000 sample, you leave it as x.

Use cross multiplication to solve from here:

100000 * 12  =  1500 * x
1200000  =  1500x
x = 800

There are 800 iPhones expected to be defective in a sample of 100,000.

Answer 2

Well i'm not sure how you're supposed to do it but if it were me:

1500/12 = 125
so then divide 100,000 by 125 and you'll get 800. 

hope this would help