Why are the values of t and u?
(geometry question)

t = 18, u = 123

Step-by-step explanation:

The external angle of a triangle is equal to the sum of the 2 opposite interior angles.

7t - 23 is an exterior angle of the triangle, thus

7t - 23 = 49 + 3t ( subtract 3t from both sides )

4t - 23 = 49 ( add 23 to both sides )

4t = 72 ( divide both sides by 4 )

t = 18

7t - 23 and u - 46 are adjacent angles and supplementary, thus

7t - 23 + u - 46 = 180 ← substitute t = 18

7(18) + u - 69 = 180

126 + u - 69 = 180

57 + u = 180 ( subtract 57 from both sides )

u = 123

x= cost per bracelet

number of bracelets * x + shipping charge = total cost

so

9x+9=72