Answer :
5g + 3(-7 + 5g) = 1 - g
5g - 21 + 15g = 1 - g
20g - 21 = 1 - g
20g + g = 1 + 21
21g = 22
g = 22/21 <===
5g - 21 + 15g = 1 - g
20g - 21 = 1 - g
20g + g = 1 + 21
21g = 22
g = 22/21 <===