Mark has less than 20.00 to spend on the cost of dinner

Midpoint formula : m = (x1 + x2) / 2 , (y1 + y2) / 2
midpoint is (6,4)
one point is (2,1)...x1 = 2 and y1 = 1

(6,4) = (2 + x2) / 2 , (1 + y1)/2

so 2 + what divided by 2 = 6
(2 + x) / 2 = 6
2 + x = 6 * 2
2 + x = 12
x = 12 - 2
x = 10

and 1 + what divided by 2 = 4..
(1 + y)/2 = 4
1 + y = 4 * 2
1 + y = 8
y = 8 - 1
y = 7

so ur other endpoint is : (10,7)