Answer:
The twins would be 13 years old.
Step-by-step explanation:
21+21+21+13+13 = 89
The line y = mx + c has a slope of m.
Parallel line:
A parallel line will also have a slope of m, and should be of the form
y = mx + k
Because the line passes through the point (a,b), therefore
ma + k = b
k = b - ma
The equation of a parallel line is
y = mx + b - ma
= m(x-a) + b
Perpendicular line:
A perpendicular line will have a slope of -1/m, because the product of slopes should be -1.
The equation for a perpendicular line is of the form
y = -(1/m)x + k
Because the line passes through (a,b), therefore
-(1/m)a + k = b
k = b + a/m
The equation for a perpendicular line is
y = -(x/m) + b + a/m
= -(1/m)(x-a) + b
Answer:
Parallel line:

Perpendicular line:
Okay I will have an example for you. 3 and 2/7. STEP 1) multiply the denominator by the whole number. 3×7=21. STEP 2) add the numerator to 21. 21+2=23. STEP 3) 23 is the new numerator so put 23 over 7. FINAL SOLUTION 23/7.
There's an app called photomath that would be useful for these kinds of problems!