Logan genetically engineered a new type of fir tree and a new type of pine tree. The combined height of one fir tree and one pine tree is 21 meters. The height of 4 fir trees stacked on top of each other is 24 meters taller than one pine tree. How tall are the types of trees that Logan genetically engineered?

Let f be the height of the fir trees

Let p be the height of the pine trees

We know from the problem that

f + p = 21 and 4f = 24 + p

rearrange the 2nd equation to get p = 4f - 24 and substitute into the other equation

so ...

f + 4f - 24 = 21

5f - 24 = 21

5f = 45

f = 9 - height of the fir tree

substitute back into the 1st equation

9 + p = 21

p = 12 - height of the pine tree