The total height of Bill, Mary, and Rob is 180 cm. Rob is twice as tall as Bill and Mary is 28 cm taller than Bill. How tall is Rob?

Rob is 76 cm tall.

Step-by-step explanation:

Let b = height of bill.

Let m = height of Mary.

Let r = height of Rob.

"the total heigh of bill mary and rob is 180 cm"

b + m + r = 180 Equation 1

"bob * is twice as tall as bill"

*I think you meant Rob is twice as tall as Bill.

r = 2b

"mary is 28 cm taller than bill"

m = b + 28

Substitue r = 2b and m = b + 28 into Equation 1.

b + b + 28 + 2b = 180

4b + 28 = 180

4b = 152

b = 38

r = 2b

r = 2 (38) = 76

Rob is 76 cm tall.

76 cm

Step-by-step explanation:

The total height is 180 cm. We set Bill as x. Rob is 2x. Mary is 28+x.

x + 2x + (28+x) = 180

4x + 28 = 180

4x = 152

x = 38

This means that Bill is 38 cm. Rob is 2x.

2x = 2 (38) = 76