Step-by-step explanation:
notice that 29 is one smaller than 30 and is being multiplied by 31. it is one smaller times 31 so 900 - 31 = 869. 31 is one bigger multiplied by 29 so 869 + 29 = 898. plus 1 = 899
25 times 25 = 625
625 - 26 = 599
599 + 24 = 623
plus 1 = 624