kasih jalan ya kak, tolong nih

no. 13
5x+3y = 21 |×2|
4x+2y = 16 |×3|

10x+6y = 42
12x+6y = 48
_________ _
-2x = -6
x = 3

4x+2y = 16
4(3)+2y = 16
12+2y = 16
2y = 4
y = 2

x+5 = 3+5 = 8 (c)

no.14
x-y = 7
x+3y = 3
______ _
-4y = 4
y = -1

x-y = 7
x-(-1) = 7
x = 7-1
x = 6

7x+2y = 7(6)+2(-1) = 42 - 2 = 40 (c)