Question

$\triangle abc \cong \triangle adc$. find $y$.

Explanation:

Step1: Set congruent sides equal

$5y - 7 = 3y + 21$

Step2: Subtract $3y$ from both sides

$5y - 3y - 7 = 21$
$2y - 7 = 21$

Step3: Add 7 to both sides

$2y = 21 + 7$
$2y = 28$

Step4: Divide by 2

$y = \frac{28}{2}$

Answer:

$14$