{[(4×n+26) : 42 ] ×15 - 10} : 5 = 7
[(4×n+26) : 42 ] ×15 - 10 = 5×7
[(4×n+26) : 42 ] ×15 - 10 = 35
[(4×n+26) : 42 ] ×15 = 35+10
[(4×n+26) : 42 ] ×15 = 45
(4×n+26) : 42 = 45 : 15
(4×n+26) : 42 = 3
4×n+26 = 3×42
4×n +26 = 126
4×n = 126-26
4×n = 100
n = 100:4
n = 25