Ols regression predictions

#1
Hello everyone,
Do i have to use the formula 1)y=b+b1x1+b2x2+b3x3
=81+0.48*50+0.46*30+0.06*100
=124.8
b1= age b2=BMI b3=blood glucose b=constant


2)
Difference =b1*(difference in x1)
=0.48*20
=9.6




Is this correct or am i doing something wrong?

Thanks.
 

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