Question 665619
Let c = cat's weight
Let d = dog's weight
Since we have two unknowns we need two equations to solve the problem.
From the problem statement  we have
(1) d = 6*c and
(2) d + c = 98
This is called a system of equations to find it in your text book. One of the simplist ways to solve this type of problem is by "substitution", wherein we solve one equation for one of the variable in terms of the other variable. Then replace that variable in the second equation with the resulting expression. In your case you already have d in terms of c given by (1), so you merely replace d in (2) with (1) and get
(3) 6*c + c = 98, ok?
or
(4) 7*c = 98 or
(5) c = 98/7 or
(6) c = 14
Using (2) with c = 14 we get
(7) d + 14 = 98 or
(8) d = 98 - 14 or
(9) d = 84
Are these values correct? Let's check using (1).
Is (84 = 6*14)?
Is (84 = 84)? Yes
Answer: Ricardo's dog weights 84 pounds.