Grandpa Xiaodong's age is minus 15, divided by 4, minus 6, and finally multiplied by 10 equals 100. How old is grandpa Xiaodong?

If the backward method is adopted, multiplying by 10 equals 100, which is10;

Subtracting 6 equals 10, which is16;

Divided by 4 equals 16, which is 64;

Subtracting 15 equals 64, which is 79.