To solve this problem, we can follow the order of operations (parentheses, exponents, multiplication/division, addition/subtraction) to simplify the expression step by step:

7 1/7 15 3/4 28:
First, convert the mixed numbers to improper fractions:
7 1/7 = 50/7
15 3/4 = 63/4

Perform the multiplication:
(50/7) (63/4) = (50 63) / (7 * 4) = 3150 / 28

Next, simplify the result:
3150 / 28 = 112.5

5:4
This is equivalent to 5 divided by 4:
5 / 4 = 1.25

2 12
2 12 = 24

5 * 10 5/9
First, convert the mixed number to an improper fraction:
10 5/9 = 95/9

Now, perform the multiplication:
5 (95/9) = (5 95) / 9 = 475 / 9

Therefore, the expression simplifies to:
112.5 1.25 24 * 475/9

To calculate the final answer, we need to multiply all the numbers together:
112.5 1.25 24 475/9 = 1125 24 475 / (9 100)

Now perform the multiplication:
1125 24 475 = 12750000

And finally, divide by 900:
12750000 / 900 = 14166.67

Therefore, the final answer is approximately 14166.67.