I believe what the problem means is that the height of the child, if he/she grows in height, the mesurements are equal to 1 ft, 2 ft, 3 ft, 4 ft, etc only. and no decimals or fractions in between. it is also said that a human stops growing at the age of 20 naturally, hence with this increment, a child can grow incredibly very tall.
60/8 = 7.4. The dog is faster. 35/5 = 7
Well your c value is already there (6) as the standard equation for a line is
y = mx + c
To find the gradient (M) plot two points on the line.
Then label each co ordinate X1 and X2 and then Y1 and Y2
Then subtract your y1 from y2 and then x1 from x2.
For example :if your coordinates were (1,2) (3,4) you would do
4-2 and 3-1
These answers become your “changes” now do change in y / change in x
In terms of the Example you would do 2/2 which would be 1 and the M value would be 1
Hope that isn’t too confusing