The answer is: 10 x¹³ y¹⁰ .
__________________________________________________________
1x^8 * 2y^(10) * 5x^5 =
1* 2* 5 * x^8 * x^5 * y^(10) =
10 * x^(8+5) * y^(10) =
10 * x^(13) * y^(10) = 10 x^(13) y^10 ; write as:
_______________________________________________
10 x¹³ y¹⁰ .
______________________________________________________