Question

{(72:a+4x3)x6-5x19}+(126x6-339:3)=668                                                   (n:5-5)x9+248:8=2x20

Answer 1

{(72:a+4x3)x6-5x19}+(126x6-339:3)=668
{(72:a+12)x6-95}+(756-113)=668 
{(72:a+12)x6-95}+643=668 
(72:a+12)x6-95=668 -643
(72:a+12)x6-95=25
(72:a+12)x6=25+95
(72:a+12)x6=120
72:a+12=20
72:a=20-12
72:a=8
a=9

(n:5-5)x9+248:8=2x20
(n:5-5)x9+31=40
(n:5-5)x9=40-31
(n:5-5)x9=9
n:5-5=1
n:5=6
n=30

Answer 2

{[72/a+12]·6-95}+[756-113]=668;
⇒[72/a+12]·6-95+643=668
⇒[72/a+12]·6-95=25
⇒[72/a+12]·6=120
⇒72/a+12=20
⇒72/a=8⇒a=9;

[n/5-5]·9+31=40
⇒[n/5-5]·9=9
⇒[n/5-5]=1
⇒n/5=6
⇒n=30;