we know that a area of a triangle is base x height divided by 2. So we multiply the value of the base than the height of the unit of the base which contains 37x11 and then divide by 2 to get the inside of the triangle unit.
First you have to multiply 42 times 3 to find the total age of the three people. Then multiply 40 times 4 to find the age of the four people in all. Subtract.