The given formula 
Solve for y means we have to make y alone
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Add -10 on both sides, we get

As there is multiplication sign between r and y so to solve for y, divide both side by r

Part A: c for cost. c=0.31m+0.5
0.31m is the cost per minute. 0.5 is cost per call.
Part B: 0.31m+0.5=5.15 to solve we must rearrange.
subtract 0.5 from each side giving us 0.31m=4.85
divide by 0.31 giving us m=15.65
We know that
scale factor=measure larger triangle/measure smaller triangle---->18/12
scale factor=1.5
so
measure larger triangle=scale factor*measure smaller triangle
for the leg in the smaller triangle equal to 5
measure larger triangle=1.5*5-----> 7.5
the answer is
7.5
A polynomial function is a function involving only non-negative (positive and 0) integer powers of 'x', i.e. all terms with ' 'x' have a non-negative integer power, such as a quadratic
and so on.
Option E is the answer.
Rest all are wrong answers. they do not have positive integers.