Three nuts and six bolts have a combined mass of 72g. four nuts and five bolts have a combined mass of 66g. find the mass of one nut and one bolt

3n + 6b = 72...multiply by 4
4n + 5b = 66 ...multiply by -3

12n + 24b = 288 (result of multiplying by 4)
-12n - 15b = - 198 (result of multiplying by -3)
add
9b = 90
b = 90/9
b = 10 each bolt is 10 grams

3n + 6b = 72
3n + 6(10) = 72
3n + 60 = 72
3n = 72 - 60
3n = 12
n = 12/3
n = 4each nut is 4 grams

so the mass of 1 bolt and 1 nut = 10 + 4 = 14 grams <==

200.96 is the answer