$6894.986 + 5025.005 + 600.020 = ?$

If a six-digit number $53a29b$ is divisible by $88$,then find the value of $a$ and $b$.

$(21.98)^{2} - (25.02)^{2} + (13.03)^{2} = ?$

The product of three consecutive even numbers is $4032$. The product of the first and the third number is $252$. What is five times the second number?

The digits indicated by $^*$ in $3422213^{**}$ so that this number is divisible by $99$ are

The difference between one-fourth of a number and one-seventh of the same number is $24$. What is the number?