To answer this you just need to come up with the equation for the line that passes through the points (0,32) and (10,50) Use the C temperatures as your x values and the F temperatures as your y values.
Put this in the form y=mx+b where m is the slope and b is the y intercept. Since we have the point (0,32) we know the y intercept is 32.
y=mx+32
We can calculate the slope by taking rise over run which would be 18/10 which can be reduced to 9/5 so the equation for this line is
y=9/5x+32 and it looks like this
To get the degrees Fahrenheit when degrees Celsius equals 30 we need to plug in 30 for the x value in the equation and then solve for y
y=9/5(30)+32
simplify this by multiplying and adding
y=54+32
y=86
So 30 degrees celsius is equal to 86 degrees Farenheit.