Answer:
7. 37
8. 74
9. 402
10. 74
Explanation:
You can simplify the expressions and then do the substitution of the variable value, or you can simply plug in the numbers and do the arithmetic. Either way takes about the same effort.
7. 3(5·4 -1) -4(3·4 -7) = 3·19 -4·5 = 57 -20 = 37
8. 3(5·4 -6) +4(20 -3·4) = 3·14 +4·8 = 74
9. 5(10r +3) -7r = 50r +15 -7r = 43r +15 = 43·9 +15 = 402
10. 4(5r -3) -2(6r -7) = 20r -12 -12r +14 = 8r +2 = 8·9 +2 = 74