We can notice that the first entry of each of the pairs of numbers is increasing by 3
12, x, 18, 21
So, we expect x=15
And, similarly, in the case of the second entry
32,40,48,y
Notice that they increase by 8 (32+8=40, 40+48=48), then y=48+8=56
We already have x and y, we only need to find the proportional relationship
For this, we can plot the points on a plane, as the follow drawing:
It's a line!
Writing down its equation:
In general, given two points in a line, the equation of a line is given by:
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