To factor by grouping, you basically just split the equation into 2 groups (you can only group when you have an even amount of numbers, but this problem did that for you so you’re good!)
Now, your two groups are (35xy-5x) and (-56y+8). Here, you want to find the largest common denominator from the numbers inside the parenthesis, to make the two equations the same.
From (35xy-5x) you can take out an x, and 5. By taking out 5x and leaving it on the outside of the equation, that makes this 5x(7y-1).
Next, you have to find a way to make (-56y+8) equal to (7y-1), since they have to be the same. you can take out -8! by taking out -8, you get -8(7y-1). the two equations inside the parenthesis are the same, which is good!
Now that you have (7y-1) as the first part of your factored equation, combine the two numbers you removed from the groups, 5x and -8. This makes your factored equation (5x-8)(7y-1), which should be your final answer! I hope this helped :)
