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<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

.parent {
  width: 100%;
  display: flex;
}

.child {
  margin: 5px;
  width: 25%;
  border: 2px solid red;
  background: silver;
/*   14px = margin*2 +  border*2 */
  padding-bottom: calc(25% - 14px);
}

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