The calculation process is as follows:

1, carefully observe the equation:: 2 3 = 9; 7￥2= 15; 3￥5=25;

2. Discovery rule: 2 3 = 2+3+4 = 9; 7￥2=7+8= 15; 3￥5=3+4+5+6+7=25;

3. The law of this equation is:? 2 3 means the addition of three consecutive natural numbers with 2 as the first addend. 72 represents the addition of two consecutive natural numbers with 72 as the first addend. 3 5 means the addition of five consecutive natural numbers with 3 as the first addend;

4. According to the law, 16 4 refers to the addition of four consecutive natural numbers with 16 as the first addend; That is164 =16+17+18+19 = 70;

5. So, the answer is 70;

Extended data:

The skills of finding laws in mathematics are:

1, and find the increment from n- 1 to n-th;

2. Find the total increase from 1 to the nth place;

3. The 1 bit of the sequence plus the total increment is the nth bit.

There are many mathematical thinking methods in junior high school mathematics, the most basic and main ones are: reduction thinking method, combination of numbers and shapes thinking method, classified discussion thinking method, function and equation thinking method and so on.