aim how we solve proportions by using cross products

The Term cross product it helps me remember the how to solve a proportion its makes me define by multiplying the denominator with the numeration and it give me the product just b cross multiply
The error in these steps is that they cross multiply wrong that why there a error with that steps it have a variable and they did it as they didn't have a variable as in is perfectly full of numbers
the problem is ratios cause that is one way to write a ratios
they are proportion because 6x15 equal too 90 and 2x 45 it equals 90 so they both proportion