Take a look at the constants first. Each is a multiple of 5, so 5 is a factor and we can write:
Now the contents of the parentheses. xy² is a common factor because the lowest power of x is 1, making x a factor; and the lowest power of y is 2, making y² a factor, so we combine x with y² to get factor xy², which joins 5 outside the parentheses:
5xy²(2x+3y-1), when we reduce the powers of x by 1 and y by 2. So the HCF is 5xy². It’s the highest common factor because it combines all the other common factors into one.