For a polynomial of the form ax² - bx + c rewrite the middle term as a sum of two terms whose product is a·c=10·-10 = -100 and whose sum is b= 21.
We factor 21 out of 21y.

Rewrite 21 as −4 plus 25.

Apply the distributive property.

Factor the highest common denominator of each group. Group the first two terms and the last two.

Factor the highest common denominator (GCF) of each group.

Factor the polynomial by factoring the greatest common denominator, 5y-2.

The answer is: (5y - 2)(2y + 5)