Question

a)
a+b=20, b+c=30
3×a+7×b+4×c


b)
a+b=33, a+c=11
5×a+3×b+2×c


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Answer 1

3a+3b+4b+4c=3×(a+b)+4×(b+c)=3×20+4×30=60+120=180

3a+2a+3b+2c=3×(a+b)+2×(a+c)=3×33+2×11=99+22=121

Answer 2

a)
1.
30-20=10
20-10=10
30-10=20

3×a+7xb+4×c=30+70+80=180

b)
1.33-11=22
33-22=11
22-11=11

5×a+3xb+2xc=55+33+44=132