Let x = the number of 1 pt shots made
Then x + 15 = the number of 2 pt shots made
Since there were a total of 43 baskets made, then the # of 3 pt shots is equal to:
total number of shots made minus the sum of 1 and 2 pt shots, which algebraically speaking is
43 - (x + (x + 15)) = 43 - (2x + 15) = 28 - 2x = # of 3 pt shots made
Now, we can set up the following equations:
x(1) + (x + 15)(2) + (28 - 2x)(3) = 78 (the total number of points)
x + 2x + 30 + 84 - 6x = 78
3x + 114 - 6x = 78
114 - 3x = 78
-3x = -36
x = 12
So, there were 12 one point shots made
(x + 15) = 12 + 15 = 27 two point shots made
and
28 - 2x = 28 - 2(12) = 28 - 24 = 4 three pt shots made