So
a be first term and d be common difference
- a+a+2d+a+4d+a+6d+a+9d=17
- 5a+21d=17--(1)
And
- a+d+a+3d+a+5d+a+7d+a+9d=15
- 5a+25d=15--(2)
Eq(1)-Eq(2)
Put in second one
- 5a+25d=15
- a+5d=3
- a+5/2=15
- a=15-5/2
- a=25/2
F=\dfrac{9}{5}C+32\\\\A.\\\dfrac{9}{5}C+32=F\ \ \ |-32\\\\\dfrac{9}{5}C=F-32\ \ \ |\cdot\dfrac{5}{9}\\\\C=\dfrac{5}{9}(F-32)
B.\\F=212\to C=\dfrac{5}{9}(212-32)=\dfrac{5}{9}\cdot180=100\\\\212^oF=100^oC
C.\\F=80\to C=\dfrac{5}{9}(80-32)=\dfrac{5}{9}\cdot48\approx26.7\\\\80^oF\approx26.7^oC
Answer:

Step-by-step explanation:
1) Change the mixed fractions into improper fractions:
2) Multiply the first fraction by 2/2 and the second fraction by 5/5 in order to create common factors on the denominator (You can do this because you are essentially multiplying by one, for example 2/2 = 1):

3) Simplify the numerator(top part) while keeping the denominator(bottom part) the same:
